huao

#include<cstdio>
#include<cmath>
int main(){
    double x1,x2,y1,y2,M;
    scanf("%lf %lf\n",&x1,&y1);
    scanf("%lf %lf\n",&x2,&y2);
    M=sqrt((x2-x1)*(x2-x1)+(y1-y2)*(y1-y2));
    printf("%.4lf",M);

    return 0;
}