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

int main()
{
    float xa, xb, xc, ya, yb, yc;
    scanf("%f %f %f %f %f %f",&xa,&ya,&xb,&yb,&xc,&yc);
    float res=sqrt(((xb-xa)*(xb-xa)+(yb-ya)*(yb-ya))*((xc-xa)*(xc-xa)+(yc-ya)*(yc-ya)))/2;
    printf("%.7f", res);
    return 0;
}