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

int main(void)
{
	double a, b, c, d, e;

	scanf("%lf,%lf,%lf,%lf", &a, &b, &c, &d);

	e = sqrt((a - c)*(a - c) + (b - d)*(b - d));
	
	printf("%lf", e);

	return 0;
}
