Find first bad version

Solution to Find first bad version problem.

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        if (n < 0)
            return n;
        if (n==0)
            return isBadVersion(0) ? 0 : -1;
        
        int l=0, r=Integer.MAX_VALUE;
        int lastBad = -1;
        while(l<=r) {
            int m = l + (r-l)/2;
            
            if (isBadVersion(m)) { // Check for older bad version.
                lastBad=m;
                r=m-1;
            } else { // versions till m are fine. Check versions greater than m.
                l=m+1;
            }
        }
        
        return lastBad;
    }
}