#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

int main(){
    int c, in, out;
    cin >> c >> in >> out;
    cout << fixed << setprecision(6) << pow((out - in)/2., 2) * (in + out) * M_PI * M_PI * c << endl;
}