#include<stdio.h>
#include<stdlib.h>
int main()
{
    int j=-1;
  int n; scanf("%d",&n); 
  char *str=(char*)malloc((n+1)*sizeof(char)); 
  scanf("%s",str);
  char position; scanf(" %c",&position);
  for(int i=0;i<n;i++){
    if(str[i]==position){j=i; break;}
  }
  printf("%d",j);
  free(str);
    return 0;
}
简单易懂