#include <iostream>
#include <string>
using namespace std;

int main() {
    int N, K, cnt = 0;
    string S;
    cin >> N >> K >> S;
    char c = S[--K];
    while (cnt >= 0) cnt += S[++K] == c ? 1 : -1;
    cout << K + 1 << endl;
    return 0;
}