#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;
}