package contest;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

public class Q190_2 {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
	
	void solve()
	{
		long n = nl(), L = Math.max(n, nl()), R = Math.min(6*n, nl());
		
		if(n <= 3000){
			if(L > Integer.MAX_VALUE / 3){
				out.printf("%.14f\n", 0.);
				return;
			}
			double[] dp = new double[20000];
			dp[0] = 1;
			for(int i = 0;i < n;i++){
				for(int j = 19999;j >= 0;j--){
					if(dp[j] > 0){
						for(int k = 1;k <= 6;k++){
							dp[j+k] += dp[j] / 6;
						}
						dp[j] = 0;
					}
				}
			}
			double ret = 0;
			for(int i = Math.max(0, (int)L);i <= R && i < 20000;i++){
				ret += dp[i];
			}
			out.printf("%.14f\n", ret);
		}else{
			double mu = 3.5*n;
			double sigma = 0;
			for(int i = 1;i <= 6;i++)sigma += (i-3.5)*(i-3.5);
			sigma /= 6;
			sigma = Math.sqrt(sigma*n);
//			tr(mu, sigma);
//			double all = (erf((6*n+0.5-mu)/Math.sqrt(2)/sigma) - erf((n-0.5-mu)/Math.sqrt(2)/sigma))/2;
//			all = 1;
			double sup = erf((R+0.5-mu)/Math.sqrt(2)/sigma);
			double inf = erf((L-0.5-mu)/Math.sqrt(2)/sigma);
			out.printf("%.14f\n", (sup-inf)/2/1);
		}
	}
	
	double erf(double x)
	{
		if(x < -50)return -1;
		if(x > 50)return 1;
		return 2./Math.sqrt(Math.PI)*simpson(0, x, 500000);
	}
	
	public static double simpson(double l, double r, int k)
	{
		double h = (r-l)/(2*k);
		double fo = 0, fe = 0;
		for(int i = 1;i <= 2*k-3;i+=2){
			fo += f(l+h*i);
			fe += f(l+h*(i+1));
		}
		return (f(l)+f(r)+4*(fo+f(r-h))+2*fe)*h/3;
	}
	
	public static double f(double x)
	{
		return Math.exp(-x*x);
	}

	
	void run() throws Exception
	{
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
	}
	
	public static void main(String[] args) throws Exception { new Q190_2().run(); }
	
	private byte[] inbuf = new byte[1024];
	private int lenbuf = 0, ptrbuf = 0;
	
	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }
	
	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private char[][] nm(int n, int m)
	{
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private int ni()
	{
		int num = 0, b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}