#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    double c, a, b;
    cin >> c >> a >> b;

    double ans = (b - a) * (b - a) / 4.0 * 3.14159265358979 * (b + a) * 3.14159265358979 * c;

    cout << fixed << setprecision(10) << ans << endl;
    return 0;
}