#include<stdio.h>
//二分法实现数组查找
 
//
int recurbinary(int *a, int key, int low, int high)
{
    int mid;
    if(low > high)
        return -1;
    mid = (low + high)/2;
    if(a[mid] == key) return mid;
    else if(a[mid] > key)
         return recurbinary(a,key,low,mid -1);
    else
         return recurbinary(a,key,mid + 1,high);
 
}

int binary( int *a, int key, int n )
{
    int left = 0, right = n - 1, mid = 0;
    mid = ( left + right ) / 2;
    while( left < right && a[mid] != key )
    {
        if( a[mid] < key ) {
            left = mid + 1;
        } else if( a[mid] > key ) {
            right = mid - 1;
        }
        mid = ( left + right ) / 2;
    }
    if( a[mid] == key )
        return mid;
    return -1;
}
 
int main(void)
{
int a[10] = {2,4,6,8,10,12,14,16,18,20},t,k,f;
scanf("%d",&t);
k = recurbinary(a,t,2,20);
f = binary(a,t,10);  //非递归算法
if(k == -1){
printf("不存在此数\n");
}else{
printf("%-5d是数组第%d个元素\n%-5d数组的第%d个元素",k,k+1,f,f+1);
}
 
return 0;
}