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

int main(void)
{
	double a, x1, x2, y1, y2;

	scanf("%lf,%lf,%lf,%lf", &x1, &x2, &y1, &y2);

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

	return 0;
}
