#include<stdio.h>
int binary_search(int arr[],int N,int age)
{
    int low=0,high=N-1;
    while(low<=high)
    {
        int mid=(low+high)/2;
        if(arr[mid]==age)
            return mid+1;
        else if(arr[mid]<age)
            low=mid+1;
        else
            high=mid-1;
    }
    return -1;
}
int main()
{
    int N;
    scanf("%d",&N);
    if(N<=1||N>=10)
    {
        printf("Invalid input");
        return 0;
    }
    int arr[N];
    for(i=0;i<N;i++)
        scanf("%d",arr[i]);
    int age;
    sacnf("%d",&age);
    if(age<=1||age>=100)
    {
        printf("Invalid input");
        return 0;
    }
    int result=binary_search(arr,N,age);
    printf("%d",result);
    return 0;
}