#include <stdio.h>
int main() 
{
    int n;
    int found=0;
    scanf("%d",&n);
    int arr[n];
    for(int i=0;i<n;i++)
    {
        scanf("%d",&arr[i]);
    }
    
    int key;
    scanf("%d",&key);
    int low=0;
    int high=n-1;
    while(low<=high)
    {
        int mid=(low+high)/2;
        if(arr[mid]==key)
        {
            printf("%d",i);
            found=1;
            break;
        }
        else(arr[mid]<key)
        {
            low=mid+1;
        }
        else
        {
            high=mid-1;
        }
   
    }
    if(!found)
    {
        printf("element not found");
        return 0;
    }
    
}