// URL: https://yukicoder.me/problems/no/302

import std.algorithm, std.array, std.container, std.math, std.range, std.typecons, std.string;
import std.mathspecial;

version(unittest) {} else
void main()
{
  long N; io.getV(N);
  long L, R; io.getV(L, R);

  if (L > N*6) io.put!"{exit: true}"(0);

  if (N < 5000) {
    auto dp = new double[][](N+1, N*6+2);
    foreach (dpi; dp) dpi[] = 0;
    dp[0][0] = 1;

    foreach (i; 0..N) {
      foreach (j; 0..i*6+1) {
        dp[i+1][j+1] += dp[i][j]/6;
        dp[i+1][j+7] -= dp[i][j]/6;
      }
      foreach (j; 1..(i+1)*6+1)
        dp[i+1][j] += dp[i+1][j-1];
    }

    io.put(dp[N][L..R+1].sum);
  } else {
    auto mu = 7.0/2*N, sigma = sqrt(35.0/12*N);
    io.put((erfc(-(R+0.5-mu)/(sqrt(2.0)*sigma))-erfc(-(L-0.5-mu)/(sqrt(2.0)*sigma)))/2);
  }
}

auto io = IO!()();
import std.stdio;
struct IO(alias IN = stdin, alias OUT = stdout)
{
  import std.conv, std.format, std.meta, std.traits, core.stdc.stdlib;

  auto getV(T...)(ref T v) { foreach (ref w; v) get(w); }
  auto getA(T)(size_t n, ref T v) if (hasAssignableElements!T)
  { v = new T(n); foreach (ref w; v) get(w); }
  auto getC(T...)(size_t n, ref T v)
  if (allSatisfy!(hasAssignableElements, T))
  {
    foreach (ref w; v) w = new typeof(w)(n);
    foreach (i; 0..n) foreach (ref w; v) get(w[i]);
  }
  auto getM(T)(size_t r, size_t c, ref T v)
  if (hasAssignableElements!T && hasAssignableElements!(ElementType!T))
  { v = new T(r); foreach (ref w; v) getA(c, w); }
  template getS(E...)
  {
    auto getS(T)(size_t n, ref T v)
    { v = new T(n); foreach (ref w; v) foreach (e; E) mixin("get(w."~e~");"); }
  }

  const struct PutConf
  {
    bool newline = true, flush, exit;
    string floatFormat = "%.10f", delimiter = " ";
  }

  auto put(alias conf = "{}", T...)(T v)
  { mixin("const PutConf c = "~conf~"; putMain!c(v);"); }
  auto putB(alias conf = "{}", S, T)(bool c, S t, T f)
  { if (c) put!conf(t); else put!conf(f); }
  auto putRaw(T...)(T v) { OUT.write(v); OUT.writeln; }

  private
  {
    dchar[] buf;
    auto sp = (new dchar[](0)).splitter;
    void nextLine() { IN.readln(buf); sp = buf.splitter; }
    auto get(T)(ref T v) { if (sp.empty) nextLine(); v = sp.front.to!T; sp.popFront(); }

    auto putMain(PutConf c, T...)(T v)
    {
      foreach (i, w; v) {
        putOne!c(w);
        if (i < v.length-1) OUT.write(c.delimiter);
      }
      static if (c.newline) OUT.writeln;
      static if (c.flush) OUT.flush();
      static if (c.exit) exit(0);
    }
    auto putOne(PutConf c, T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putRange!c(v);
      else if (isFloatingPoint!T) OUT.write(format(c.floatFormat, v));
      else OUT.write(v);
    }
    auto putRange(PutConf c, T)(T v)
    {
      auto w = v;
      while (!w.empty) {
        putOne!c(w.front); w.popFront();
        if (!w.empty) OUT.write(c.delimiter);
      }
    }
  }
}