#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; const constexpr int INF = 1e9; #define FOR(i, a, n) for (ll i = (ll)a; i<(ll)n; ++i) #define REP(i, n) FOR(i, 0, n) typedef long long ll; typedef vector VI; typedef pair P; struct Less{ bool operator()(const pair&a, const pair&b){ if(a.first==b.first){ return a.second < b.second; } return a.first < b.first; } }; const constexpr ll MOD = 1e9 + 7; ll extGCD(ll a, ll b, ll& x, ll& y){ if(b==0){ x=1; y=0; return a; } ll d = extGCD(b, a%b, y, x); y -= a/b*x; return d; } ll GCD(ll a, ll b){ if(b==0) return a; return GCD(b, a%b); } int main() { double C, Rin, Rout; cin >> C >> Rin >> Rout; double r=(Rout-Rin)/2; double gx = Rin + r; cout << fixed << setprecision(10) << C*2*M_PI*gx*r*r*M_PI << endl; return 0; }