#include<stdio.h>
int main(){
    
    int n;
    double x1,x2,y1,y2;
    double D;
    
    if(scanf("%d",&n)!=1){
        printf("Invalid input");
        return 0;
    }
    else{
        for(int i=0;i<=n;i++){
            if(scanf("%lf %lf %lf %lf",&x1,&x2,&y1,&y2)!=4){
             printf("Invalid input");
             return 0;
            }
    
                D=sqrt((x2-x1)*(x2-x1) +(y2-y1)*(y2-y1));
                printf("%.2lf",D);
                return 0;
            
            
        }
    }
    
}