import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
T[] RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[][] RDA2(T = long)(size_t n, T[] fix = []) { auto r = new T[][](n); foreach (i; 0..n) { r[i] = readln.chomp.split.to!(T[]); foreach (j, e; fix) r[i][j] += e; } return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * (y / gcd(x, y)); }

//long mod = 10^^9 + 7;
long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{
	auto N = RD;
	auto M = RD;
	auto st = new long[][](M, 2);
	foreach (i; 0..M)
	{
		auto s = RD-1;
		auto t = RD-1;
		st[i] = [s, t];
	}

	auto edges = new long[][](N);
	foreach (j; 0..M)
	{
		edges[st[j][0]] ~= st[j][1];
	}

	double dfs(long pos, bool[] used, double[long] memo)
	{
		if (pos == N-1) return 1.0;
		if (used[pos]) return -1.0;
		if (memo.get(pos, -1.0) != -1.0) return memo[pos];

		used[pos] = true;
		double res = 0.0;
		foreach (v; edges[pos])
		{
			auto r = dfs(v, used, memo);
			//debug writeln("u:", pos, " v:", v, " r:", r);
			if (r == -1.0) return r;
			res += r;
		}
		used[pos] = false;
		if (edges[pos].empty)
		{
			memo[pos] = -1.0;
			return -1.0;
		}
		else if (pos == 0)
		{
			memo[pos] = res / edges[pos].length;
			return res / edges[pos].length;
		}
		else
		{
			memo[pos] = res / edges[pos].length + 1.0;
			return res / edges[pos].length + 1.0;
		}
	}

	double ans = double.max;
	{
		double[long] memo;
		auto r = dfs(0, new bool[](N), memo);
		if (r != -1.0)
			ans = min(ans, r);
	}
	foreach (i; 0..M)
	{
		edges = new long[][](N);
		foreach (j; 0..M)
		{
			if (i == j) continue;
			edges[st[j][0]] ~= st[j][1];
		}
		double[long] memo;
		auto r = dfs(0, new bool[](N), memo);
		if (r != -1.0)
			ans = min(ans, r);
		debug writeln("i:", i, " ans:", ans);

	}
	
	writefln(FMT_F, ans);
	stdout.flush();
	debug readln();
}