#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

const double PI = acos(-1.0);

int main()
{
    int c, r1, r2;
    cin >> c >> r1 >> r2;

    double v = pow((r2 - r1) / 2.0, 2.0) * ((r2 + r1) / 2.0) * pow(PI, 2.0) * 2.0;
    double ret = v * c;
    printf("%.10f\n", ret);

    return 0;
}