#include <bits/stdc++.h> using namespace std; int main() { int x1,x2,y1,y2; double a,b,c; cin>>x1>>y1>>x2>>y2; a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)); b=fabs(x1-x2)+fabs(y1-y2); c=fabs(a-b); cout<<fixed<<setprecision(10)<<c<<endl; } // 64 位输出请用 ...