#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> Pr;

int N, K;
string s;

int main()
{
	cin >> N >> K >> s;
	char c = s[K - 1];
	int c_num = 0,ans;

	for (int i = K; i < s.size(); i++) {
		if (c == s[i]) 
			c_num++;
		else {
			if (c_num == 0) {
				ans = i + 1;
				break;
			}
			else 
				c_num--;
		}
	}
	cout << ans << endl;
	return 0;
}