#include <iostream>
#include <cassert>
using namespace std;
int BinarySearch(const char* a,int n,char x);
int main()
{
    int len = 0;
    cin>>len;
    char arr[len];
    char aim;
    cin>>arr>>aim;
    if(BinarySearch(arr,len,aim)!=-1)
        cout<<BinarySearch(arr,len,aim);
    else cout<<"Error";
}
int BinarySearch(const char* a,int n,char x)
{
    assert(a);
    int begin = 0;
    int end = n;
    while(begin < end)
    {
        int mid = begin+((end-begin)>>1);
        if(a[mid]<x)
            begin = mid+1;
        else if(a[mid]>x)
            end = mid;
        else
            return mid;
    }

    return -1;
}

    return -1;
}