#include<iostream>
#include<vector>
#include<algorithm>
#include<cctype>
#include<utility>
#include<string>
#include<cstring>
#include<cmath>
#include<numeric>
#include<queue>
#include<climits>
#include<cstdio>


#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)
//#define INF ((LLONG_MAX) / (2))
using namespace std;
typedef pair<int, int> P;
typedef pair<llong, llong> LP;
typedef pair<int, P> PP;
typedef pair<llong, LP> LPP;
typedef long long int ll;
typedef pair<ll,int> LL_IP;
typedef pair<ll,ll> LL_LLP;
#define INF 1e9+7
#define ARRAY_MAX 100005

int main(){

    int c,Rin,Rout;
    cin >> c >> Rin >> Rout;

    double ans = pow(M_PI,2)*(pow(Rout,2)-pow(Rin,2))*(Rout-Rin)*c/4;

    printf("%.7f\n",ans);
}