#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long ll;
using namespace std;
const int inf = 1e9+7;

int C,Ri,Ro;
int main() {
    cin>>C>>Ri>>Ro;
    double R=(Ri+Ro);
    double r=(Ro-Ri)/2.0;
    double ans=(M_PI*r*r)*(M_PI*R)*C;
    printf("%.6f\n",ans);
    return 0;
}