#include <iostream>
using namespace std;
int main() {
    int i,j,s,aux,x[100];
    for (i=1;i<=4;i++)
        cin>>x[i];
    for (i=1;i<=4;i++)
        for (j=i+1;j<=4;j++)
        if (x[i]>x[j]) {
            aux=x[i];
            x[i]=x[j];
            x[j]=aux;
        }
    s=(x[4]*x[3])+(x[2]*x[1]);
    cout<<s;
    return 0;
    }