#include <stdio.h>
#include <math.h>

int main()
{
    double x[2], y[2];

    while (scanf("%lf%lf%lf%lf", x[0], y[0], x[1], y[1]) != EOF)
        printf("%.2f\n", sqrt((x[1]-x[0])*(x[1]-x[0]) + (y[1]-y[0])*(y[1]-y[0])));

    return 0;
}