#include<stdio.h>
int main()
{
    int a,b,c,x,y,z,total_cost;
    scanf("%d %d",&a,&x);
    scanf("%d %d",&y);
    scanf("%d %d",&z);
    total_cost=(a*x)+(b*y)+(c*z);
    if(a<=0&&b<0&&c<=0&&x<=0&&y<=0&&z<=0)
    {
        printf("Invalid input\n");
    }
    else
    {
        printf("%d\n",total_cost);
    }
    return 0;
}