#include<bits/stdc++.h>
using namespace std;
int main(){
    int N,K; cin>>N>>K;
    string S; cin>>S;
    int last=N-1;
    S="o"+S;
    for(int i=N-1;i>=0;i--){
        if(last-i>K&&S[i]=='o') last=i;
    }
    cout<<last<<endl;
}