ural 1294 Mars Satellites

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
const double eps=1e-8;

int main()
{
    double a,b,c,d;
    scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
    a*=1000.0; b*=1000.0; c*=1000.0; d*=1000.0;
    if(fabs(c*d-a*b)<eps)
    {
        printf("Impossible.
");
    }
    else
    {
        printf("Distance is %.0lf km.
",sqrt((c*d*(a*a+b*b)-a*b*(c*c+d*d))/(c*d-a*b)));
    }
    return 0;
}