#include <iostream>
#include <string.h>
#include <stdio.h>
#include <algorithm>
using namespace std;
int main(){ 
	int n,sum=-1;
	string s;
	cin>>n>>s;
	char a;
	cin>>a; 
	for(int j=0;j<n;j++)
	{
		if(a == s[j])
		{
		sum=j;break;
		}			 
	}
	cout<<sum;
	return 0;
}