Submission #7962990

---

Source Code Expand

#include <bits/stdc++.h>
using namespace std;

int main()
{
	int R, N, M;
	cin >> R >> N >> M;

	vector<long double> rr( N + 1 );
	if( N % 2 == 0 ) {
		for( int i = 1; i < N; i++ ) {
			rr[i] = (long double)2 * R * abs( N / 2 - i) / N;
			rr[i] *= rr[i];
		}
	}
	else {
		for( int i = 1; i < N; i++ ) {
			rr[i] = (long double)2 * R * min( abs( N / 2 - i ), abs( N / 2 + 1 - i ) ) / N + (long double)R / N;
			rr[i] *= rr[i];
		}
	}
	long double ans = 0;
	long double rr2 = (long double)R * R;
	for( int i = 1; i <= N + M - 1; i++ ) {
		long double l1 = 0;
		if( i < N ) {
			l1 = sqrt( rr2 - rr[i] );
		}
		long double l2 = 0;
		if( i - M > 0 ) {
			l2 = sqrt( rr2 - rr[i - M] );
		}
		long double l3 = max( l1, l2 );
		ans += l3 * 2;
	}

	cout << fixed << setprecision(12) << ans << endl;
}

Submission Info

Judge Result