#include <bits/stdc++.h>
#define rep(i,n) for(int i=0; i<(int)(n); i++)

using namespace std;
const int Max_N=2e5;
const int INF=1e9;

int main(){
	int N, K;
	cin >> N >> K;
	string S;
	cin >> S;
	assert(1<=K && K<N);
	assert(N<=Max_N);
	assert(S.size()==N-1);
	rep(i,N-1) assert(S[i]=='o' || S[i]=='x');

	int ans=INF;
	for(int i=N-2; i>=0; i--){
		if(S[i]=='x') continue;		
		if(ans-i<=K) continue;
		ans=i;
	}
	if(ans+1>K) cout << 0 << endl;
	else cout << ans+1 << endl;

	return 0;
}