//https://ncode.syosetu.com/n4830bu/302/
#include <bits/stdc++.h>
using namespace std;

int main() {
    long long N, L, R;
    cin >> N >> L >> R;
    if (N < 10000) {
        vector<long double> dp(N * 6 + 10);
        dp[0] = 1;
        for (int _ = 0; _ < N; _++) {
            vector<long double> dp_nxt(N * 6 + 10);
            for (int i = 0; i < N * 6; i++) {
                for (int j = 1; j <= 6; j++) {
                    dp_nxt[i + j] += dp[i] / 6;
                }
            }
            swap(dp_nxt, dp);
        }
        long double ans = 0;
        for (int i = L; i <= min(N * 6, R); i++) {
            ans += dp[i];
        }
        cout << fixed << setprecision(10) << ans << endl;
    } else {
        auto maine = [&](long double x) {
            long double mu = 3.5 * N, sigma = sqrt(35.0 / 12 * N);
            return (1.0l + erf((x - mu) / sqrt(2) / sigma)) / 2.0l;
        };
        cout << fixed << setprecision(10) << maine(R + 0.5) - maine(L - 0.5) << endl;
    }
}