class Solution {
public:
    int guessNumber(int n)
    {
        int pick=search(1,n);
        return pick;
    }
private:
    //binary search algo
    int search(int s,int e)
    {  
        int pick=0;
        while(s<=e)
        {
            int m=s + (e-s)/2;
            if(guess(m)==0)
            {
                pick=m;
                break;
            }
            else if(guess(m)==-1)
            {
                e=m-1;
            }
            else if(guess(m)==1)
            {
                s=m+1;
            }
        }
        return pick;
    }
};