#include<iostream>
using namespace std;

int main(){
  int n,x=0;
  cin>>n>>x;
  char a[n+1];
  cin>>a;
  
  for(int i=0;i<n;i++){
    if(a[i]=='o'){
      x++;
    }else if(a[i]=='x' && x!=0){
      x--;
    }
  }
  
  cout<<x;
return 0;
}
#include <iostream>
#include <math.h>
#include <string>
#include <vector>
#include <algorithm>
//#include <bits/stdc++.h>
using namespace std;

int main()
{
    long long a, b, c;
    cin >> a >> b >> c;
    cout << 21 - (a + b + c);
    return 0;
}