#include<iostream>
using namespace std;

int main()
{
	int i,j;
	float aux, v[4];
	for(i=1;i<=4;i++)
		cin>>v[i];
	for (i = 1; i <= 4; i++)
    {
        for (j = 1; j <= 4; j++)
        {
            if (v [i] > v [j])
            {
                aux = v [i];
                v [i] = v [j];
                v [j] = aux;
            }
		}
	}
	cout<<v[1]*v[2]+v[3]*v[4];
	return 0;
}