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