180427_2959_거북이

	//https://www.acmicpc.net/problem/2959 #include <iostream>
	#include <algorithm>
	using namespace std;
	int main(){
	int n[4];
	for(int i=0; i<4; i++) cin >> n[i];
	sort(n, n+4);
	cout << n[0]*n[2];
	return 0;
	}