#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n, k;
    string s;
    cin >> n >> k;
    cin >> s;

    char t = s[k - 1];
    int c = 0;
    for (int i = 0; i < k; i++) {
        if (s[i] == t) {
            c++;
        } else {
            c--;
        }
    }

    int c2 = 0;
    for (int i = n - 1; i >= 0; i--) {
        if (s[i] != t) {
            c2++;
        } else {
            c2--;
        }

        if (c == c2) {
            cout << i + 1;
            break;
        }
    }

    return 0;
}