#include <iostream>

using namespace std;
int v[4],s;

int main()
{

	for (int i = 0; i < 4; i++){
		cin >> v[i];
	}
	for (int i = 0; i < 3; i++)
		for (int j = i + 1; j < 4;j++)
			if (v[j]>v[i]){
			s = v[i];
			v[i] = v[j];
			v[j] = s;
			}
	cout << v[0] * v[1] + v[2] * v[3];

	return 0;
}