{{{#!highlight haskell
#include<stdio.h>
#include<math.h>
int main(){

float x1,y1,x2,y2;

scanf("%f %f %f %f",&x1,&y1,&x2,&y2);
printf("%f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));

return(0);
}
}}}