#include <cstdio>
#include <algorithm>
using namespace std;

int N, i, v[6];

int main(){

//freopen("baruri.in", "r", stdin);

for(i = 1; i <= 4; i++){
    scanf("%d", &v[i]);
}sort(v + 1, v + 5);

printf("%d", v[4]*v[3]+v[2]*v[1]);

return 0;
}