#include<stdio.h>
int binarysearch(int arr[],int n,int key),{
    int low=0,high=n-1;
    while(low<=high){
        int mid=(low+high)/2;
        if(arr[mid]==key)
        return mid;
        else if(arr[mid]<key)
        low=mid+1;
        else
        high=mid-1;
    }
    return-1;
}
int main(){
    int n;
    scanf("%d",&n);
    int arr[n];
    for(int i=0;i<n;i++)
    scanf("%d"&arr[i]);
    int key;
    scanf("%d"&key);
    int result=binarysearch(arr,n,key);
    printf("%d_,result);
    return 0;
}