// editor1
#include<stdio.h>
int binary(int arr[],int n,int target)
{
    while(low<=high)
    {
        int mid=low+(high-low)/2;
        if(arr[mid]==target)
        return min;
        else if(arr[mid]<target)
        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 target;
    scanf("%d",&target);
    int result=binary(arr,n,target);
    printf("%d",result);
    return 0;
}