/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return 	     -1 if num is higher than the picked number
 *			      1 if num is lower than the picked number
 *               otherwise return 0
 * int guess(int num);
 */

int guessNumber(int n) {
    int left = 1, right = n;
    
    while (left <= right) {
        int mid = left + (right - left) / 2;
        int result = guess(mid);
        
        if (result == 0) {
            return mid;
        } else if (result == -1) {  // too high
            right = mid - 1;
        } else {  // result == 1, too low
            left = mid + 1;
        }
    }
    
    return -1;  // should never reach here
}