/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int l = 1;
        int r = n;
        while (l<=r){
            int m = l+(r-l)/2;
            if (isBadVersion(m) == true)
                r = m-1;
            else
                l = m+1;

        }
        return l;
    }
}