#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 100000000000000000


int main(){
	
	double c,r0,r1;
	cin>>c>>r0>>r1;
	
	double rd = r1-r0;
	rd /= 2.0;
	
	double ans = pow(rd,2.0) * acos(-1.0);
	
	ans *= acos(-1.0) * (r0+r1);
	
	ans *= c;
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
	return 0;
}