#include <iostream>
#include <algorithm>
using namespace std;
int w[5];
int v[5] = {0, 1, 2, 3, 4};
int main() {


    scanf("%d%d%d%d", &w[1], &w[2], &w[3], &w[4]);
    int sol = 0;
    do {
        int ss = w[v[1]] * w[v[2]] + w[v[3]] * w[v[4]];
        if (ss > sol) sol = ss;
    } while (next_permutation(v + 1, v + 5));
    printf("%d\n", sol);
    return 0;
}