#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>
#include <cstring>
#include <random>
#include <functional>
#include <numeric>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define REPLL(i,a,b) for(ll i=a;i<(ll)b;i++)
#define rep(i,n) REP(i,0,n)
#define all(c) (c).begin(), (c).end()
#define zero(a) memset(a, 0, sizeof a)
#define minus(a) memset(a, -1, sizeof a)
#define minimize(a, x) a = std::min(a, x)
#define maximize(a, x) a = std::max(a, x)

using ll  = long long;
int const inf = 1<<29;

#define double long double

int main() {

  ll N, L, R; cin >> N >> L >> R;
  L = max(N, L);
  R = min(6 * N, R);

  if(N <= 3000) {
    if(L > inf) {
      cout << "0.000000000000000000000\n";
    }

    double dp[22222]; // reuse array
    dp[0] = 1.0;
    rep(i, N) {
      for(int x=20000; x>=0; x--) {
        if(!dp[x]) { continue; }
        REP(k, 1, 7) {
          dp[x + k] += dp[x] / 6.0;
        }
        dp[x] = 0.0;
      }
    }

    double ret = 0.0;
    REPLL(i, max(0LL, L), min(R+1, 20000LL)) {
      ret += dp[i];
    }
    printf("%.15f\n", ret);
  }
  else {
    double m  = N * 3.5;
    double s  = sqrt(N * 17.5/6.0);
    double supremum = erf((R + 0.5 - m) / (sqrt(2) * s));
    double infimum  = erf((L - 0.5 - m) / (sqrt(2) * s));
    printf("%.15f\n", (supremum - infimum) / 2.0);
  }

  return 0;
}