#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
int op(int lhs, int rhs){ return max(lhs, rhs); }
int e(){ return 0; }

int main(){
    int n, k;
    string s;
    cin >> n >> k >> s;
    s = 'o' + s;
    atcoder::segtree<int, op, e> seg(vector<int>(n + 1, 1 << 30));
    for(int i = s.size() - 1, mexv; i >= 0; i--){
        if(s[i] == 'x') continue;
        seg.set(mexv = seg.max_right(0, [&](int v){return v <= i + k;}), i);
        if(!mexv && i <= k){
            cout << i << '\n';
            exit(0);
        }
    }
}