#include <iostream>
#include <string>

using namespace std;

int64_t n, k, r;
string s;
char c;

int main(){
    cin >> n >> k >> s;
    if(k<0) r+=-k, k = 0;
    for(int i = 0; i < n; ++i){
        c = s[i];
        if(c=='A') ++k;
        if(c=='C') --k;
        if(k<0&&i<n-1) ++k, ++r;
    }
    cout << r;
    return 0;

}