#include <stdio.h>

float
dotprod(int n, float x[], float y[]);

int main() {
    float a[2], b[2];
    float d;

    printf("Ax, Ay: ");
    scanf("%f, %f", &a[0], &a[1]);

    printf("Bx, By: ");
    scanf("%f, %f", &b[0], &b[1]);

    d = dotprod(2, a, b);
    printf("Dot product: %f\n", d);
    return 0;
}