#include <bits/stdc++.h>

using namespace std;

void fast_io() {
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
}

#include <atcoder/segtree>
using namespace atcoder;
using S = vector<vector<int>>;
S op(S l, S r) {
	S res(4, vector<int>(4, 1e9));
	for (int i = 0; i < 4; i++) {
		for (int j = i; j < 4; j++) {
			for (int k = j; k < 4; k++) {
				res[i][k] = min(res[i][k], l[i][j] + r[j][k]);
			}
		}
	}
	return res;
}
S e() { return S(4, vector<int>(4)); }
int main() {
	fast_io();
	int n, q;
	cin >> n >> q;
	string s;
	cin >> s;
	vector<S> seg_data(n);
	for (int i = 0; i < n; i++) {
		seg_data[i] = S(4, vector<int>(4, 1));
		for (int j = 0; j <= s[i] - 'A'; j++) {
			for (int k = s[i] - 'A'; k < 4; k++) {
				seg_data[i][j][k] = 0;
			}
		}
	}
	segtree<S, op, e> seg(seg_data);
	for (; q--;) {
		int com;
		cin >> com;
		if (com == 1) {
			int x;
			char c;
			cin >> x >> c;
			x--;
			S d(4, vector<int>(4, 1));
			for (int i = 0; i <= c - 'A'; i++) {
				for (int j = c - 'A'; j < 4; j++) {
					d[i][j] = 0;
				}
			}

			seg.set(x, d);
		} else {
			int l, r;
			cin >> l >> r;
			auto res = seg.prod(l - 1, r);
			cout << res[0][3] << "\n";
		}
	}
}