#include <stdio.h>

//written by Dan

int main()
{
	int v[4], aux, i, j;

	scanf("%d %d %d %d", &v[0], &v[1], &v[2], &v[3]);

	for (i = 0; i < 3; i++) {
		for (j = i + 1; j < 4; j++) {
			if (v[i] > v[j]) {
				aux = v[i];
				v[i] = v[j];
				v[j] = aux;
			}
		}
	}

	printf("%d", (v[0] * v[1] + v[2] * v[3]));

    return 0;
}