Find first bad version

Solution to Find first bad version problem.

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int l=1, r=n;

        while(l < r) {
            int m = l + (r - l)/2;
            if (isBadVersion(m)) 
            {
                r = m;
            } else {
                l = m + 1;
            }
        }

        return l;        
    }
}