// 
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define debug(...) fprintf (stderr, __VA_ARGS__)

#define lep(i, l, r) for (int i = (l), i##_end = (r); i <= i##_end; ++ i)
#define rep(i, r, l) for (int i = (r), i##_end = (l); i >= i##_end; -- i)

char _c; bool _f; template <class T> inline void IN (T & x) {
	x = 0, _f = 0; while (_c = getchar (), ! isdigit (_c)) if (_c == '-') _f = 1;
	while (isdigit (_c)) x = x * 10 + _c - '0', _c = getchar (); if (_f) x = - x;
}

const int mod = 998244353;
inline int mul (int x, int y) { return 1ll * x * y % mod; }
inline int qpow (int x, int y, int r = 1) { for ( ; y; y >>= 1, x = mul (x, x)) if (y & 1) r = mul (r, x); return r; }
inline void pls (int & x, int y) { x += y; if (x >= mod) x -= mod; }
inline int add (int x, int y) { x += y; if (x >= mod) x -= mod; return x; }

const int N = 5e5 + 5;

int n, m;
char str[N], fix[N];

/*
do 0
re 3
mi 2
fa 1
so 0
la 1
ti 2
*/

const char fro[] = { 'd', 'r', 'm', 'f', 's', 'l', 't' };
const int match[] = { 0, 3, 2, 1, 0, 1, 2 };
const char sub[] = { 'o', 'a', 'i', 'e' };

const int inf = 1e9 + 7;
int tr[N << 2][5][5];

inline void chkmax (int & x, int y) { if (x < y) x = y; }

inline void pushup (int x) {
	int l = x << 1, r = x << 1 | 1;
	memset (tr[x], - inf, sizeof tr[x]);
	lep (k, 0, 4) lep (i, 0, 4) lep (j, 0, 4) {
		chkmax (tr[x][i][j], tr[l][i][k] + tr[r][k][j] + (k < 4));
	}
	lep (i, 0, 4) lep (j, 0, 4) {
		chkmax (tr[x][i][j], tr[l][i][j]);
		chkmax (tr[x][i][j], tr[r][i][j]);
	}
}
void build (int x, int l, int r) {
	if (l == r) {
		memset (tr[x], - inf, sizeof tr[x]), tr[x][4][4] = 0;
		lep (i, 0, 6) if (str[l] == fro[i]) tr[x][4][match[i]] = 0;
		lep (i, 0, 3) if (str[l] == sub[i]) tr[x][i][4] = 0;
	} else {
		int mid = l + r >> 1;
		build (x << 1, l, mid);
		build (x << 1 | 1, mid + 1, r);
		pushup (x);
	}
}
void update (int x, int l, int r, int L, int R) {
	if (L > r || R < l) return ;
	if (l == r) {
		memset (tr[x], - inf, sizeof tr[x]), tr[x][4][4] = 0;
		lep (i, 0, 6) if (str[l] == fro[i]) tr[x][4][match[i]] = 0;
		lep (i, 0, 3) if (str[l] == sub[i]) tr[x][i][4] = 0;
	} else {
		int mid = l + r >> 1;
		update (x << 1, l, mid, L, R);
		update (x << 1 | 1, mid + 1, r, L, R);
		pushup (x);
	}
}

int vec[5];
void query (int x, int l, int r, int L, int R) {
	if (L <= l && r <= R) {
		vector <int> nxt (5, - inf);
		lep (i, 0, 4) lep (j, 0, 4) chkmax (nxt[j], vec[i] + tr[x][i][j]);
		lep (i, 0, 4) chkmax (vec[i], nxt[i]);
	} else {
		int mid = l + r >> 1;
		if (L <= mid) query (x << 1, l, mid, L, R);
		if (R > mid) query (x << 1 | 1, mid + 1, r, L, R);
	}
}

signed main () {
	IN (n), IN (m), scanf ("%s", str + 1);
	build (1, 1, n);
	for (int i, j; m; -- m) {
		char opt[4]; scanf ("%s", opt);
		if (opt[0] == '?') {
			IN (i), IN (j);
			memset (vec, - inf, sizeof vec), vec[4] = 0;
			query (1, 1, n, i, j);
			printf ("%d\n", (j - i + 1) - vec[4] * 2);
		} else {
			IN (i), IN (j), scanf ("%s", fix);
			lep (p, i, j) str[p] = fix[p - i];
			update (1, 1, n, i, j);
		}
	}
	return 0;
}