#include <cstdio> #include <cmath> int main() { double x1, y1, x2, y2; scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2); double distance = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); printf("%.4lf\n", distance); return 0; }