#include <bits/stdc++.h>
using namespace std;
long int a,b,res=0;
string s;
map<char,int> dict;
int main()
{
    cin >> a >> b >> s;
    dict['B'] = 0;
    dict['A'] = 1;
    dict['C'] = -1;
    for(auto i:s){
        if(b<0){
            res = 0-b;
            b=0;
        }
        b+= dict[i];
    }
     cout << res;
}