#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main() {
double x,y,z;
double zero=0;
cin>>y>>x>>z;
if ((x==y)or(z==1)){
cout<<"IMPOSSIBLE";
}else if(z==0){
cout<<y;
}else {
cout<<fixed;
cout<<setprecision(9);
zero=(y*y-x*x*z*z)/double(1-z*z);
cout<<sqrt(zero);
}
return 0;
}
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