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

float f(int a, int b) { return sqrt(a * a + b * b); }

int main() {
    int a, b, c, d;
    scanf("%d %d %d %d", &a, &b, &c, &d);
    printf("%.2f", f(a - c, b - d));
    return 0;
}