1 #include<stdio.h>
   2 #include<math.h>
   3 int main(){
   4 
   5 float x1,y1,x2,y2;
   6 
   7 scanf("%f %f %f %f",&x1,&y1,&x2,&y2);
   8 printf("%f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
   9 
  10 return(0);
  11 }