#include <bits/stdc++.h>
#define rep(i,a,n) for(int i=a;i<n;i++)
#define repb(i,a,b) for(int i=a;i>=b;i--)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

signed main(){
	double c,r,R;
	cin>>c>>r>>R;
	double ans=pow(acos(-1.0),2)*pow((R-r)/2.0,2)*(R+r);
	printf("%.10lf\n", ans);
}