/* -*- coding: utf-8 -*-
 *
 * 2992.cc:  No.2992 Range ABCD String Query - yukicoder
 */

#include<cstdio>
#include<vector>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 200000;
const int INF = 1 << 30;

/* typedef */

struct Elm {
  int ss[4][4];
  Elm(): ss() {}
  Elm(int d) {
    for (int i = 0; i < 4; i++)
      for (int j = i; j < 4; j++)
	ss[i][j] = (d < i || j < d) ? 1 : 0;
  }

  Elm operator+(const Elm &e) const {
    Elm r;
    
    for (int i = 0; i <= 4; i++)
      for (int j = i; j < 4; j++) {
	r.ss[i][j] = INF;
	for (int k = i; k <= j; k++)
	  r.ss[i][j] = min(r.ss[i][j], ss[i][k] + e.ss[k][j]);
      }

    return r;
  }

  int val() const { return ss[0][3]; }
};

template <typename T>
struct SegTreeSum {
  int e2;
  vector<T> nodes;
  T defv;
  SegTreeSum() {}

  void init(int n, T _defv) {
    defv = _defv;
    for (e2 = 1; e2 < n; e2 <<= 1);
    nodes.assign(e2 * 2, defv);
  }

  T &geti(int i) { return nodes[e2 - 1 + i]; }
  void seti(int i, T v) { geti(i) = v; }

  void setall() {
    for (int j = e2 - 2; j >= 0; j--)
      nodes[j] = nodes[j * 2 + 1] + nodes[j * 2 + 2];
  }

  void set(int i, T v) {
    int j = e2 - 1 + i;
    nodes[j] = v;
    while (j > 0) {
      j = (j - 1) / 2;
      nodes[j] = nodes[j * 2 + 1] + nodes[j * 2 + 2];
    }
  }

  T sum_range(int r0, int r1, int k, int i0, int i1) {
    if (r1 <= i0 || i1 <= r0) return defv;
    if (r0 <= i0 && i1 <= r1) return nodes[k];

    int im = (i0 + i1) / 2;
    T v0 = sum_range(r0, r1, k * 2 + 1, i0, im);
    T v1 = sum_range(r0, r1, k * 2 + 2, im, i1);
    return v0 + v1;
  }
  T sum_range(int r0, int r1) { return sum_range(r0, r1, 0, 0, e2); }
};

/* global variables */

char s[MAX_N + 4];
SegTreeSum<Elm> st;

/* subroutines */

/* main */

int main() {
  int n, qn;
  scanf("%d%d%s", &n, &qn, s);

  st.init(n, Elm());
  for (int i = 0; i < n; i++) st.seti(i, Elm(s[i] - 'A'));
  st.setall();

  while (qn--) {
    int op;
    scanf("%d", &op);

    if (op == 1) {
      int x;
      char c[4];
      scanf("%d%s", &x, c), x--;

      st.set(x, Elm(c[0] - 'A'));
    }
    else {
      int l, r;
      scanf("%d%d", &l, &r), l--;

      auto e = st.sum_range(l, r);
      printf("%d\n", e.val());
    }
  }
  
  return 0;
}