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#include<stdio.h>
#include<math.h>
int main()
{
    double d,x1,y1,x2,y2;
    while(scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2)!=EOF)
    {
    printf("%.2lf\n",d=sqrt(pow(x1-x2,2)+pow(y1-y2,2)));
    }
return 0;
}