#include <bits/stdc++.h>
#include <atcoder/segtree>
using namespace std;
using namespace atcoder;
using ll = long long;
const int inf = 1e6;

struct S {
	int AA, AB, AC, AD, BB, BC, BD, CC, CD, DD;
};

S op(S l, S r) {
	S rt;
	rt.AA = l.AA + r.AA;
	rt.AB = min(l.AA + r.AB, l.AB + r.BB);
	rt.AC = min({l.AA + r.AC, l.AB + r.BC, l.AC + r.CC});
	rt.AD = min({l.AA + r.AD, l.AB + r.BD, l.AC + r.CD, l.AD + r.DD});
	rt.BB = l.BB + r.BB;
	rt.BC = min(l.BB + r.BC, l.BC + r.CC);
	rt.BD = min({l.BB + r.BD, l.BC + r.CD, l.BD + r.DD});
	rt.CC = l.CC + r.CC;
	rt.CD = min(l.CC + r.CD, l.CD + r.DD);
	rt.DD = l.DD + r.DD;
	return rt;
}

S e() {
	return S{0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}

int main() {
	int N, Q;
	cin >> N >> Q;
	string S_;
	cin >> S_;
	vector<S> v(N);
	for (int i = 0; i < N; i++) {
		if (S_[i] == 'A') {
			v[i] = S{0, 0, 0, 0, 1, 1, 1, 1, 1, 1};
		}
		if (S_[i] == 'B') {
			v[i] = S{1, 0, 0, 0, 0, 0, 0, 1, 1, 1};
		}
		if (S_[i] == 'C') {
			v[i] = S{1, 1, 0, 0, 1, 0, 0, 0, 0, 1};
		}
		if (S_[i] == 'D') {
			v[i] = S{1, 1, 1, 0, 1, 1, 0, 1, 0, 0};
		}
	}
	segtree<S, op, e> seg(v);
	for (int i = 0; i < Q; i++) {
		int t;
		cin >> t;
		if (t == 1) {
			int x;
			char c;
			cin >> x >> c;
			x--;
			if (c == 'A') {
				seg.set(x, S{0, 0, 0, 0, 1, 1, 1, 1, 1, 1});
			}
			if (c == 'B') {
				seg.set(x, S{1, 0, 0, 0, 0, 0, 0, 1, 1, 1});
			}
			if (c == 'C') {
				seg.set(x, S{1, 1, 0, 0, 1, 0, 0, 0, 0, 1});
			}
			if (c == 'D') {
				seg.set(x, S{1, 1, 1, 0, 1, 1, 0, 1, 0, 0});
			}
		} else {
			int l, r;
			cin >> l >> r;
			l--; r--;
			cout << seg.prod(l, r + 1).AD << '\n';
		}
	}
}