module main;
// https://kmjp.hatenablog.jp/entry/2015/11/14/0930 より
// 確率、動的計画法、数値積分
import std;

void main()
{
	// 入力
	long N = readln.chomp.to!long;
	long L, R;
	readln.chomp.formattedRead("%d %d", L, R);
	// 答えの計算
	L = min(6 * N, max(N, L));
	R = min(6 * N, R);

	if (N <= 8000) {
		const di = 1 / 6.0;
		auto from = uninitializedArray!(double[])(6 * N + 10), to = from.dup;
		from[] = 0;
		from[0] = 1;
		foreach (i; 0 .. N) {
			to[] = 0;
			foreach (j; i .. 6 * i + 1)
				foreach (x; 1 .. 7)
					to[j + x] += from[j] * di;
			swap(from, to);
		}
		writefln("%.12f", from[L .. R + 1].sum);
	} else {
		double ave = N * 3.5;
		double var = N * 35.0 / 12;
		writefln("%.12f", (erf((R + 0.5 - ave) / sqrt(2 * var)) - erf((L - 0.5 - ave) / sqrt(2 * var))) / 2);
	}
}