#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <array>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<int(n); i++)
const i64 INF = 1001001001001001001;
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
using namespace std;

using Node = array<array<int,4>,4>;
Node op(Node l, Node r){
    Node res;
    rep(t,4) res[t].fill(1001001001);
    rep(i,4) for(int j=i; j<4; j++) for(int k=j; k<4; k++){
        chmin(res[i][k], l[i][j] + r[j][k]);
    }
    return res;
}


namespace nachia{

template<
    class S,
    S op(S l, S r)
>
struct Segtree {
private:
    int N;
    std::vector<S> A;
    int xN;

    void mergev(int i){
        if(i < N) A[i] = op(A[i*2], A[i*2+1]);
    }

    template<class E>
    int minLeft2(int r, E cmp, int a = 0, int b = 0, int i = -1) const {
        static S x;
        if(i == -1){ a=0; b=N; i=1; x=A[0]; }
        if(r <= a) return a;
        if(b <= r){
            S nx = op(A[i], x);
            if(cmp(nx)){ x = nx; return a; }
        }
        if(b - a == 1) return b;
        int q = minLeft2(r, cmp, (a+b)/2, b, i*2+1);
        if(q > (a+b)/2) return q;
        return minLeft2(r, cmp, a, (a+b)/2, i*2);
    }
    
    template<class E>
    int maxRight2(int l, E cmp, int a = 0, int b = 0, int i = -1) const {
        static S x;
        if(i == -1){ a=0; b=N; i=1; x=A[0]; }
        if(b <= l) return b;
        if(l <= a){
            S nx = op(x, A[i]);
            if(cmp(nx)){ x = nx; return b; }
        }
        if(b - a == 1) return a;
        int q = maxRight2(l, cmp, a, (a+b)/2, i*2);
        if(q < (a+b)/2) return q;
        return maxRight2(l, cmp, (a+b)/2, b, i*2+1);
    }

public:
    Segtree() : N(0) {}
    Segtree(int n, S e) : xN(n) {
        N = 1; while (N < n) N *= 2;
        A.assign(N * 2, e);
    }
    Segtree(const std::vector<S>& a, S e) : Segtree(a.size(), e){
        for(int i=0; i<(int)a.size(); i++) A[i + N] = a[i];
        for(int i=N-1; i>=1; i--) mergev(i);
    }

    S getE() const { return A[0]; }

    void set(int p, S x){
        p += N; A[p] = x;
        for(int d=1; (1<<d)<=N; d++) mergev(p>>d);
    }

    S get(int p) const { return A[N+p]; }

    S prod(int l, int r) const {
        l += N; r += N;
        S ql = A[0], qr = A[0];
        while(l<r){
            if(l&1) ql = op(ql, A[l++]);
            if(r&1) qr = op(A[--r], qr);
            l /= 2;
            r /= 2;
        }
        return op(ql, qr);
    }

    S allProd() const { return A[1]; }

    // bool cmp(S)
    template<class E>
    int minLeft(int r, E cmp) const {
        return minLeft2(r, cmp);
    }

    // bool cmp(S)
    template<class E>
    int maxRight(int l, E cmp) const {
        int x = maxRight2(l, cmp);
        return x > xN ? xN : x;
    }
};

} // namespace nachia

void testcase(){
    Node id;
    rep(i,4) rep(j,4) id[i][j] = i<=j ? 0 : 1001001001;
    vector<Node> K(4);
    rep(a,4){
        rep(i,4) rep(j,4) K[a][i][j] = 1001001001;
        rep(i,4) rep(j,4) if(i<=j) K[a][i][j] = (i <= a && a <= j) ? 0 : 1;
    }
    int N, Q; cin >> N >> Q;
    vector<Node> A(N);
    rep(i,N){
        char c; cin >> c;
        A[i] = K[c-'A'];
    }
    auto ds = nachia::Segtree<Node, op>(A, id);
    rep(i,Q){
        int t; cin >> t;
        if(t == 1){
            int x; cin >> x; x--;
            char c; cin >> c;
            ds.set(x, K[c-'A']);
        } else {
            int l,r; cin >> l >> r; l--;
            auto ans = ds.prod(l,r)[0][3];
            cout << ans << '\n';
        }
    }
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    testcase();
    return 0;
}