#include <iostream>
#include<utility>
#include <vector>
#include <map>
#include<string>
#include<set>
#include<queue>
#include<math.h>
#define pb push_back
#define all(x) begin(x),end(x)
#define ll long long
#define P pair<int,int>
#define lP pait<ll,ll>
using namespace std;
int main() {
    double c,ri,ro,ans,a;
    cin>>c>>ri>>ro;
    a=pow(ro-ri,2);
    ans=(ro+ri)/4*a*pow(M_PI,2)*c;
    printf("%.10lf\n",ans);
    return 0;
}