#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

// using mint = modint998244353;

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

using mint = modint1000000007;

void debug_mint1(vector<mint> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        cerr << vec[i].val() << " ";
    }
    cerr << endl;
}

void debug_mint2(vector<vector<mint>> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        for (int j = 0; j < vec[i].size(); j++) {
            cerr << vec[i][j].val() << " ";
        }
        cerr << endl;
    }
}

ll INF = 10000000000023;

vector<vector<ll>> g_vec(4, vector<ll>(4, 0));

struct S {
    vector<vector<ll>> v;
};

S op(S a, S b) {
    for (ll j = 0; j < 4; j++) {
        for (ll k = j; k < 4; k++) {
            g_vec[j][k] = INF;
        }
    }
    for (ll j = 0; j < 4; j++) {
        for (ll k = j; k < 4; k++) {
            for (ll l = k; l < 4; l++) {
                g_vec[j][l] = min(g_vec[j][l], a.v[j][k] + b.v[k][l]);
            }
        }
    }
    for (ll i = 0; i < 4; i++) {
        for (ll j = i; j < 4; j++) {
            (a.v)[i][j] = g_vec[i][j];
        }
    }
    return a;
}

S e() {
    vector<vector<ll>> ee(4, vector<ll>(4, 0));
    return S{ee};
}

int main() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    ll N, Q;
    cin >> N >> Q;
    string s;
    cin >> s;
    segtree<S, op, e> seg(N);
    for (ll i = 0; i < N; i++) {
        ll val = (ll)(s[i] - 'A');
        vector<vector<ll>> vec(4, vector<ll>(4, 0));
        for (ll j = 0; j < 4; j++) {
            for (ll k = j; k < 4; k++) {
                if (!(val >= j && val <= k)) {
                    vec[j][k] = 1;
                } else {
                    vec[j][k] = 0;
                }
            }
        }
        S sv = {vec};
        seg.set(i, sv);
    }
    for (ll i = 0; i < Q; i++) {
        ll t;
        cin >> t;
        if (t == 1) {
            ll x;
            char c;
            cin >> x >> c;
            x--;
            ll val = (ll)(c - 'A');
            vector<vector<ll>> vec(4, vector<ll>(4, 0));
            for (ll j = 0; j < 4; j++) {
                for (ll k = j; k < 4; k++) {
                    if (!(val >= j && val <= k)) {
                        vec[j][k] = 1;
                    } else {
                        vec[j][k] = 0;
                    }
                }
            }
            S sv = {vec};
            seg.set(x, sv);
        } else {
            ll L, R;
            cin >> L >> R;
            L--;
            R--;
            vector<vector<ll>> ans = seg.prod(L, R + 1).v;
            cout << ans[0][3] << "\n";
        }
    }
}