为什么不对

#include <stdio.h>

int main()

{

    double x= 13.9;

    double y =24.4;

    double sum = 0;

    double avg = 0;

    scanf("%lf%lf",&x,&y);

    sum = x+y;

    avg = sum/2;

    printf("%.2f",avg);

    return 0;

}