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