// The API isBadVersion is defined for you.
// bool isBadVersion(int version);

class Solution
{
public:
    int firstBadVersion(int n)
    {
        int left = 1;
        int right = n;
        while (left < right)
        {
            int mid = left + (right - left) / 2;
            if(isBadVersion(mid)){
                right = mid;
            }else{
                left = mid+1;
            }
        }
        return left;
    }
};