#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){
        printf("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");
    }
}
return 0;
}