#include<iostream>
#include<string>
using namespace std;
int main()
{
    int n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    int c = 0;
    if (k < 0)
    {
        c = -k;
        k = 0;
    }
    for(int i = 0; i < n - 1; i++)
    {
        if (s[i] == 'A') k++;
        else if (s[i] == 'C')
        {
            k--;
            if (k < 0)
            {
                c++;
                k = 0;
            }
        }
    }
    cout << c;
    system("pause");
    return 0;
}