#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>

using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
	int n;
	double a, b;
	cin>>n>>a>>b;
	double r=(1.0/(2.0*a)-1.0/(2.0*b))/2.0;
	double c;
	if(n%2==0){
		c=((double)(n-1))*r;
	}else{
		c=((double)(n/2*2))*r;
	}
	double d=sqrt((1.0/(2.0*b)+r)*(1.0/(2.0*b)+r)+c*c);
	double ans=(1.0/(d-r)-1.0/(d+r))/2.0;
	printf("%.6lf\n", ans);
	return 0;
}