LeetCode 278. First Bad Version

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

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