ural 1294 Mars Satellites

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

 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.\n");
     }
     else
     {
         printf("Distance is %.0lf km.\n",sqrt((c*d*(a*a+b*b)-a*b*(c*c+d*d))/(c*d-a*b)));
     }
     return ;
 }