import std.algorithm, std.conv, std.range, std.stdio, std.string;
import std.math;
import std.mathspecial;

// allowable-error: 10 ** -5

void main()
{
  auto n = readln.chomp.to!long;
  auto rd = readln.split.to!(long[]), l = rd[0], r = rd[1];

  writefln("%.6f", n < 5000 ? calc1(n, l, r) : calc2(n, l, r));
}

auto calc1(long n, long l, long r)
{
  auto m = n * 6;

  auto dp = new real[][](n+1, m+1);
  foreach (ref dpi; dp) dpi[] = 0;
  dp[0][0] = 1;
  
  foreach (i; 1..n+1)
    foreach (j; 1..m+1)
      dp[i][j] = dp[i-1][max(0, j-6)..j].sum / 6;

  return dp[n][min(l, r)..min(m, r)+1].sum;
}

auto calc2(long n, long l, long r)
{
  auto u = 7.0 / 2 * n, s2 = 35.0 / 12 * n;
  return (erf((r+0.5 - u) / sqrt(s2 * 2)) - erf((l-0.5 - u) / sqrt(s2 * 2))) / 2;
}