import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


long N, L, R;

void main() {
  try {
    for (; ; ) {
      N = readLong();
      L = readLong();
      R = readLong();
      real ans;
      if (N <= 5000) {
        const lim = cast(int)(N) * 6;
        auto dp = new real[lim + 1];
        dp[] = 0.0;
        dp[0] = 1.0;
        foreach (i; 0 .. N) {
          foreach_reverse (x; 0 .. lim + 1) {
            dp[x] = dp[max(x - 6, 0) .. x].sum / 6.0;
          }
        }
        ans = 0.0;
        foreach (x; 0 .. lim + 1) {
          if (L <= x && x <= R) {
            ans += dp[x];
          }
        }
      } else {
        import std.mathspecial : erf;
        const e = 3.5L * cast(real)(N);
        const v = (35.0L / 12.0L) * cast(real)(N);
        const s = sqrt(v);
        ans = (erf((cast(real)(R) + 0.5 - e) / (sqrt(2.0L) * s)) - erf((cast(real)(L) - 0.5 - e) / (sqrt(2.0L) * s))) / 2.0;
      }
      writefln("%.20f", ans);
    }
  } catch (EOFException e) {
  }
}