#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;



template<class T, T (*add)(T, T), T (*zero)(), T (*mul)(T, T), T (*one)(), int N>
struct Mat : array<array<T, N>, N> {
  using M = Mat<T, add, zero, mul, one, N>;
  void make_identity() {
    for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++) {
        (*this)[i][j] = zero();
      }
    }
    for (int i = 0; i < N; i++) {
      (*this)[i][i] = one();
    }
  }
  M& operator+=(const M& rhs) {
    for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++) {
        (*this)[i][j] = add((*this)[i][j], rhs[i][j]);
      }
    }
    return *this;
  }
  M& operator*=(const M& rhs) {
    static M temp;
    for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++) {
        temp[i][j] = zero();
      }
    }
    for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++) {
        for (int k = 0; k < N; k++) {
          temp[i][k] = add(temp[i][k], mul((*this)[i][j], rhs[j][k]));
        }
      }
    }
    *this = temp;
    return *this;
  }
  template <class I>
  void inplace_pow(I k) {
    assert(k >= 0);
    static M temp;
    temp = *this;
    make_identity();
    while (k) {
      if (k & 1) *this *= temp;
      k >>= 1;
      if (k) temp *= temp;
    }
  }
  friend ostream& operator<<(ostream& os, const M& A) {
    for (int i = 0; i < N; i++) {
      for (int j = 0; j < N; j++) {
        os << A[i][j] << " \n"[j + 1 == N];
      }
    }
    return os;
  }
};

constexpr int INF = 1001001001;
int add(int x, int y) { return min(x, y); }
int zero() { return INF; }
int mul(int x, int y) { return x + y; }
int one() { return 0; }

using M = Mat<int, add, zero, mul, one, 4>;

M e() {
  M res;
  res.make_identity();
  return res;
}
M op(M a, M b) {
  M c = a;
  c *= b;
  return c;
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, q;
  cin >> n >> q;
  string s;
  cin >> s;
  vector<M> init(n);
  auto make_M = [&](char c) {
    M a;
    rep(i, 4) rep(j, 4) a[i][j] = INF;
    int x = c - 'A';
    rep(i, 4) rep(j, 4) if (i <= j) {
      a[i][j] = !(i <= x && x <= j);
    }
    return a;
  };
  rep(i, n) {
    init[i] = make_M(s[i]);
  }
  segtree<M, op, e> seg(init);
  rep(_, q) {
    int type;
    cin >> type;
    if (type == 1) {
      int x;
      char c;
      cin >> x >> c;
      x--;
      s[x] = c;
      seg.set(x, make_M(c));
    } else {
      int l, r;
      cin >> l >> r;
      l--;
      auto a = seg.prod(l, r);
      int res = INF;
      rep(j, 4) chmin(res, a[0][j]);
      cout << res << '\n';
    }
  }
}