#include <bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<(b);++i)
using namespace std;
using pii = pair<int,int>;
using ll = long long;
using pll = pair<ll,ll>;
using vi = vector<int>;
 
using ld = long double;
 
#define all(x) (x).begin(), (x).end()
 
const int maxn = 1e6+10, inf = 1e9+100;
const ll linf = 1e18+100;
const int mod = 998244353;
 
const ld eps = 1e-9;
const ld PI = acos(-1.L);

using Matrix = array<array<int,8>,8>;
using Vector = array<int,8>;

string tar[8] = {"", "do", "re", "mi", "fa", "so", "la", "ti"};

Matrix mval[26];
Matrix getmat(char c) {
  Matrix m;
  for(int i=0;i<8;i++)for(int j=0;j<8;j++)m[i][j] = -inf;
  for(int i=0;i<8;i++)m[i][i] = 0;
  for(int i=1;i<8;i++){
    if(tar[i][0] == c) m[i][0] = 1;
    if(tar[i][1] == c) m[0][i] = 1;
  }
  return m;
}

Matrix mult(const Matrix& a, const Matrix& b) {
  Matrix c;
  for(int i=0;i<8;i++)for(int j=0;j<8;j++)c[i][j] = -inf;
  for(int i=0;i<8;i++)for(int j=0;j<8;j++)for(int k=0;k<8;k++){
    c[i][k]=max(c[i][k],a[i][j]+b[j][k]);
  }
  return c;
}

Vector mult(const Matrix& a, const Vector& b) {
  Vector c;
  for(int i=0;i<8;i++)c[i] = -inf;
  for(int i=0;i<8;i++)for(int j=0;j<8;j++){
    c[i]=max(c[i],a[i][j]+b[j]);
  }
  return c;
}

const int maxnodes = (1 << 19) + 100;
Matrix seg[maxnodes];

string s;

const int thres = 2;

void init(int x,int l,int r) {
  if(r-l<thres) {
    seg[x] = mval[s[l]-'a'];
    for(int i=l+1;i<=r;i++)seg[x]=mult(mval[s[i]-'a'],seg[x]);
  }
  else {
    int mid = (l+r)/2;
    init(x*2,l,mid);
    init(x*2+1,mid+1,r);
    seg[x] = mult(seg[x*2+1],seg[x*2]);
  }
}

void upd(int x,int l,int r,int a, char c) {
  if(r-l<thres) {
    s[a]=c;
    seg[x] = mval[s[l]-'a'];
    for(int i=l+1;i<=r;i++)seg[x]=mult(mval[s[i]-'a'],seg[x]);
  }
  else {
    int mid = (l+r)/2;
    if(a<=mid)upd(x*2,l,mid,a,c);
    else upd(x*2+1,mid+1,r,a,c);
    seg[x] = mult(seg[x*2+1],seg[x*2]);
  }
}

Vector ans;
void qu(int x,int l,int r,int a,int b) {
  if(l==a&&r==b) {
    ans = mult(seg[x], ans);
  }
  else if(r-l<thres) {
    for(int i=a;i<=b;i++){
      ans = mult(mval[s[i]-'a'], ans);
    }
  }
  else {
    int mid = (l+r)/2;
    if(b<=mid)qu(x*2,l,mid,a,b);
    else if(a>mid)qu(x*2+1,mid+1,r,a,b);
    else {
      qu(x*2,l,mid,a,mid);
      qu(x*2+1,mid+1,r,mid+1,b);
    }
  }
}

void solve(){
  int n,q;
  cin >> n >> q;
  cin >> s;
  for(int i=0;i<26;i++){
    mval[i] = getmat('a'+i);
  }
  init(1,0,n-1);
  for(int i=0;i<q;i++){
    string ty;
    cin >> ty;
    if(ty == "?") {
      int a,b;
      cin >> a >> b;
      a--,b--;
      ans[0] = 0;
      for(int i=1;i<8;i++)ans[i] = -inf;
      qu(1,0,n-1,a,b);
      cout << (b-a+1) - ans[0] << "\n";
    }
    else {
      int a,b;
      string t;
      cin >> a >> b >> t;
      // cerr << a << " " << b << " " << t << endl;
      a--,b--;
      for(int i=0;i<t.size();i++){
        // cerr << a << " " << t[a+i] << endl;
        upd(1,0,n-1,a+i,t[i]);
      }
    }
  }
}
 
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout<<fixed;
  cout.precision(20);
  cerr << fixed;
  cerr.precision(5);
  solve();
}