#include<bits/stdc++.h> #include<cmath>//不能缺少这个头文件 using namespace std; int main(){ double x1,y1,x2,y2; cin>>x1>>y1; cin>>x2>>y2; double t1 = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));//求平方根的和 printf("%0.4f",t1); return 0; }