#include <bits/stdc++.h>
#include <atcoder/all>


using namespace std;
using namespace atcoder;
#define rep(i,m,n,k) for (int i = (int)(m); i < (int)(n); i += (int)(k))
#define rrep(i,m,n,k) for (int i = (int)(m); i > (int)(n); i += (int)(k))
#define ll long long
#define list(T,A,N) vector<T> A(N);for(int i=0;i<(int)(N);i++){cin >> A[i];}

template <class T>
map<T,ll> Counter(vector<T> A){
    map<T,ll> m;
    for(auto a:A) m[a]++;
    return m;
} 


int main(){
    
    long double C,R,r;
    cin >> C >> r >> R;
    long double pi = 3.14159265358979;
    long double ans;
    ans = C*pi*pi*(r+R)*((R-r)/2)*((R-r)/2);
    
    cout << fixed << setprecision(10);
    cout << ans << endl;
    return 0;
}