#include <iostream>

using namespace std;

int main() {
	int a,b,c,d,aux;
	
	cin>>a>>b>>c>>d;
	
	if (c<d) {
		aux = c; c = d; d = aux;
	}

	if (b<c) {
		aux = b; b = c; c = aux;
	}

	if (a<b) {
		aux = a; a = b; b = aux;
	}
	
	if (c<d) {
		aux = c; c = d; d = aux;
	}

	if (b<c) {
		aux = b; b = c; c = aux;
	}

	if (c<d) {
		aux = c; c = d; d = aux;
	}
	
	cout<<a*b+c*d;
	
	return 0;
}