#include<stdio.h>
int main(){
    int qx, px, qy, qz, pz;
    if(scanf("%d %d", &qx, &px) != 2) {
        printf("Invalid input");
        return 0;
    }
    if(scanf("%d %d", &qz, &pz) != 2) {
        printf("Invalid input");
        return 0;
    }
    if (qx < 0 || px < 0 || qy < 0 || pz < 0 || qz < 0 || pz < 0) {
        printf("Invalid input");
        return 0;
    }
    int total = qx * px + qy * py + qz * pz;
    return 0;
}