#include <cstdio>
#include <algorithm>

using namespace std;

int a[7], Ans;

int main(){
    scanf("%d %d %d %d", &a[1], &a[2], &a[3], &a[4]);
    int v[] ={0, 1, 2, 3, 4};
    while(next_permutation(v + 1, v + 5)){
        Ans = max(Ans, a[v[1]] * a[v[2]] + a[v[3]] * a[v[4]]);
    }
    printf("%d", Ans);
    return 0;
}