#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

#ifdef _MSC_VER
#include <intrin.h>
#endif

namespace atcoder {

namespace internal {

// @param n `0 <= n`
// @return minimum non-negative `x` s.t. `n <= 2**x`
int ceil_pow2(int n) {
    int x = 0;
    while ((1U << x) < (unsigned int)(n)) x++;
    return x;
}

// @param n `1 <= n`
// @return minimum non-negative `x` s.t. `(n & (1 << x)) != 0`
constexpr int bsf_constexpr(unsigned int n) {
    int x = 0;
    while (!(n & (1 << x))) x++;
    return x;
}

// @param n `1 <= n`
// @return minimum non-negative `x` s.t. `(n & (1 << x)) != 0`
int bsf(unsigned int n) {
#ifdef _MSC_VER
    unsigned long index;
    _BitScanForward(&index, n);
    return index;
#else
    return __builtin_ctz(n);
#endif
}

}  // namespace internal

}  // namespace atcoder

namespace atcoder {

template <class S, S (*op)(S, S), S (*e)()> struct segtree {
  public:
    segtree() : segtree(0) {}
    explicit segtree(int n) : segtree(std::vector<S>(n, e())) {}
    explicit segtree(const std::vector<S>& v) : _n(int(v.size())) {
        log = internal::ceil_pow2(_n);
        size = 1 << log;
        d = std::vector<S>(2 * size, e());
        for (int i = 0; i < _n; i++) d[size + i] = v[i];
        for (int i = size - 1; i >= 1; i--) {
            update(i);
        }
    }

    void set(int p, S x) {
        assert(0 <= p && p < _n);
        p += size;
        d[p] = x;
        for (int i = 1; i <= log; i++) update(p >> i);
    }

    S get(int p) const {
        assert(0 <= p && p < _n);
        return d[p + size];
    }

    S prod(int l, int r) const {
        assert(0 <= l && l <= r && r <= _n);
        S sml = e(), smr = e();
        l += size;
        r += size;

        while (l < r) {
            if (l & 1) sml = op(sml, d[l++]);
            if (r & 1) smr = op(d[--r], smr);
            l >>= 1;
            r >>= 1;
        }
        return op(sml, smr);
    }

    S all_prod() const { return d[1]; }

    template <bool (*f)(S)> int max_right(int l) const {
        return max_right(l, [](S x) { return f(x); });
    }
    template <class F> int max_right(int l, F f) const {
        assert(0 <= l && l <= _n);
        assert(f(e()));
        if (l == _n) return _n;
        l += size;
        S sm = e();
        do {
            while (l % 2 == 0) l >>= 1;
            if (!f(op(sm, d[l]))) {
                while (l < size) {
                    l = (2 * l);
                    if (f(op(sm, d[l]))) {
                        sm = op(sm, d[l]);
                        l++;
                    }
                }
                return l - size;
            }
            sm = op(sm, d[l]);
            l++;
        } while ((l & -l) != l);
        return _n;
    }

    template <bool (*f)(S)> int min_left(int r) const {
        return min_left(r, [](S x) { return f(x); });
    }
    template <class F> int min_left(int r, F f) const {
        assert(0 <= r && r <= _n);
        assert(f(e()));
        if (r == 0) return 0;
        r += size;
        S sm = e();
        do {
            r--;
            while (r > 1 && (r % 2)) r >>= 1;
            if (!f(op(d[r], sm))) {
                while (r < size) {
                    r = (2 * r + 1);
                    if (f(op(d[r], sm))) {
                        sm = op(d[r], sm);
                        r--;
                    }
                }
                return r + 1 - size;
            }
            sm = op(d[r], sm);
        } while ((r & -r) != r);
        return 0;
    }

  private:
    int _n, size, log;
    std::vector<S> d;

    void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); }
};

}  // namespace atcoder

using namespace std;

typedef long long ll;
#define all(x) begin(x), end(x)
constexpr int INF = (1 << 30) - 1;
constexpr long long IINF = (1LL << 60) - 1;
constexpr int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

template <class T> istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) is >> x;
    return is;
}

template <class T> ostream& operator<<(ostream& os, const vector<T>& v) {
    auto sep = "";
    for (const auto& x : v) os << exchange(sep, " ") << x;
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = forward<U>(y), true); }

template <class T> void mkuni(vector<T>& v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <class T> int lwb(const vector<T>& v, const T& x) { return lower_bound(begin(v), end(v), x) - begin(v); }

const int MAX = 4;
using ARR = array<array<int, MAX>, MAX>;
const vector<string> cand = {"do", "re", "mi", "fa"};

struct st {
    ARR dp;
    st(ARR dp) : dp(dp) {}
};

st op(st l, st r) {
    ARR dp;
    for (int i = 0; i < MAX; i++) {
        for (int k = 0; k < MAX; k++) {
            dp[i][k] = (i == k ? 0 : -INF);
            for (int j = 0; j < MAX; j++) {
                if (l.dp[i][j] < 0 or r.dp[j][k] < 0) continue;
                dp[i][k] = max(dp[i][k], l.dp[i][j] + r.dp[j][k]);
            }
        }
    }
    return st(dp);
}

st e() {
    ARR dp;
    for (int i = 0; i < MAX; i++) {
        for (int j = 0; j < MAX; j++) {
            dp[i][j] = (i == j ? 0 : -INF);
        }
    }
    return st(dp);
}

char g(char c) {
    if (c == 's') c = 'd';
    if (c == 'l') c = 'f';
    if (c == 't') c = 'm';
    return c;
}

st f(char c) {
    c = g(c);
    ARR dp;
    for (int i = 0; i < MAX; i++) {
        for (int j = 0; j < MAX; j++) {
            dp[i][j] = (i == j ? 0 : -INF);
            if (i == 0) {
                if (j == 0) continue;
                if (c == cand[j - 1][0]) dp[i][j] = 1;
            } else {
                if (j > 0) continue;
                if (c == cand[i - 1][1]) dp[i][j] = 1;
            }
        }
    }
    return dp;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, q;
    string S;
    cin >> n >> q >> S;

    vector<st> init;
    for (int i = 0; i < n; i++) init.emplace_back(f(S[i]));
    atcoder::segtree<st, op, e> seg(init);
    auto query = [&](int l, int r) {
        auto res = seg.prod(l, r).dp;
        return (r - l) - res[0][0];
    };
    for (; q--;) {
        char c;
        cin >> c;
        if (c == '?') {
            int l, r;
            cin >> l >> r;
            cout << query(--l, r) << '\n';
        } else {
            int i, j;
            string T;
            cin >> i >> j >> T;
            i--;
            for (int k = i; k < j; k++) seg.set(k, f(T[k - i]));
        }
    }
    return 0;
}