#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <sstream>
#include <string>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
#define var auto
#define mod 1000000007
#define inf 2147483647
#define nil -1
typedef long long ll;

using namespace std;

inline int input(){
    int a;
    cin >> a;
    return a;
}

template <typename T>
inline void output(T a, int p) {
    if(p){
        cout << fixed << setprecision(p)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

// end of template

int main() {
    cin.tie(0);
    // source code
    ll N, L, R;
    cin >> N >> L >> R;
    R = min(R, 6 * N);
    double p = 1.0 / 6;
    if (N <= 2000) {
        vector<double> tmp(6 * N + 1), dp(6 * N + 1);
        tmp[0] = 1;
        rep(i, N){
            dp.assign(6 * N + 1, 0);
            rep(j, 6 * N + 1){
                repd(k, 1, 7){
                    dp[j + k] += tmp[j] * p;
                }
            }
            tmp = dp;
        }
        
        double ret = 0;
        for (ll i = L; i <= R; i++) {
            ret += dp[i];
        }
        output(ret, 15);
    }
    else{
        double mu = 7.0 / 2 * N;
        double sigma = 35.0 / 12 * N;
        double ret = 1.0 / 2 * (erf((R + 0.5 - mu) / sqrt(2 * sigma)) - erf((L - 0.5 - mu) / sqrt(2 * sigma)));
        output(ret, 15);
    }
    
    
    
    
    return 0;
}