这个怎么改呀

#include <stdio.h>
#include <math.h>
int distance(double x1, double x2, double y1, double y2) {
    double m = 0;
    m = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
    double add = 0;
    add = sqrt(m);
    return add;
}
int main() {
    double a1, a2, b1, b2, c1, c2;
    scanf("%lf %lf", &a1, &a2);
    scanf("%lf %lf", &b1, &b2);
    scanf("%lf %lf", &c1, &c2);
    double m, n, j;
    m = distance(a1, a2, b1, b2);
    n = distance(a1, a2, c1, c2);
    j = distance(b1, b2, c1, c2);
    printf("%.2f", m + n + j);
    return 0;
}