#include <stdio.h> #include <math.h> #include using namespace std; int main() { double x1,x2,y1,y2; cin >> x1 >> y1 >> x2 >>y2; double a, b; a = x1 - x2; b = y1 - y2; double c; c = a * a + b * b; c = sqrt(c); printf("%.3lf\n",c); }