#include <stdio.h>

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 low=0,high=n-1,found=0;
    while(low<=high){
        int mid=(low<=high/2);
            if(arr[mid]==key){
                ptintf("element found at index %d\n",mid);
                found=1;
                break;
            }
            else if(arr[mid]<key){
                low=mid+1;
            }
            else{
                high=mid-1;
            }
    }
    if(!found){
        printf("element not found\n");
    }
    
}