#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    long long int n, k, l = 0;
    cin >> n >> k;
    string s;
    cin >> s;
    if (k < 0)
    {
        l += abs(k);
        k = 0;
    }
    for (int i=0; i<n; i++)
    {
        if (k < 0)
        {
            k++;
            l++;
        }
        if (s[i] == 'C')
            k--;
        else if (s[i] == 'A')
            k++;
    }
    cout << l << endl;
}