https://programmers.co.kr/learn/courses/30/lessons/62048

멀쩡한 사각형.java

import java.math.BigInteger;
import java.util.*;

class Solution {
    public static int gcd(int a, int b){
        BigInteger b1 = BigInteger.valueOf(a);
        BigInteger b2 = BigInteger.valueOf(b);
        return b1.gcd(b2).intValue();
    }
	public long solution(int w,int h) {
        long cutOfcircle = w+h-gcd(w, h); // 잘린 사각형
        long answer = (long)w*h-cutOfcircle;
		return answer;
	}
}