#include <stdio.h>
#include <algorithm>
#include <vector>

using namespace std;

vector<int> v;

int main() {
	v.resize(4);
	scanf("%d %d %d %d", &v[0], &v[1], &v[2], &v[3]);
	sort(v.begin(), v.end());
	printf("%d\n", v[0] * v[1] + v[2] * v[3]);
	return 0;
}