#include <iostream>

using namespace std;


int main()
{
    int v[5];
    for(int i = 1; i <= 4; i++)
        cin >> v[i];

    for(int i = 1; i <= 4; i++)
        for(int j = i + 1; j <= 4; j++)
            if(v[i] < v[j])
                {
                    int aux = v[i];
                    v[i] = v[j];
                    v[j] = aux;

                }
    cout<<v[1] * v[2] + v[3] * v[4];
    return 0;

}