sqrtx

class Solution {
public:
    int sqrt(int x) {
        int left=1,right=x/2;
        int res;
        if(x<2)return x;
        while(left<=right)
        {
            int mid=(right-left)/2+left;
            if(x/mid>mid)left=mid+1,res=mid;
            else if(x/mid<mid)right=mid-1;
            else return mid;
        }
        return res;
    }
};