1 #include<math.h>
 2 #include<stdio.h>
 3 int main()
 4 {
 5     double x1,y1,x2,y2,m;
 6     while(~scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2))
 7 //等效于  scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2)！=EOF    可以少打几个字了··· 
 8     {
 9         m=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
10         printf("%.2lf\n",m);
11     }
12     return 0;
13 }