#include<iostream>
#include<string>

using namespace std;

int main() {

	long int n, x;
	string s;
	cin>>n>>x;
	cin>>s;
	for(int i = 0; i < s.size(); i++) {

		if(s[i] == 'x' && x != 0)
			x--;
		else if(s[i] == 'o')
			x++;
	}
	cout<<x<<endl;
	return 0;
}
#include<bits/stdc++.h>
using namespace std;

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	int n,a,b;
	cin>>n>>a>>b;
	cout<<n-a+b;
}