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

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
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; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

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; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); }
double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; }

long mod = 10^^9 + 7;
//long mod = 998_244_353;
//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 modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }
void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); }

void main()
{
	auto N = RD;
	auto M = RD;
	auto edges = new long[][](N);
	auto par = new bool[long][](N);
	auto chi = new bool[long][](N);
	foreach (i; 0..M)
	{
		auto U = RD-1;
		auto V = RD-1;
		edges[U] ~= V;
		par[V][U] = true;
		chi[U][V] = true;
	}

	auto used = new bool[](N);
	foreach (i; 0..N)
	{
		if (par[i].empty && chi[i].empty)
			used[i] = true;
	}

	long[] l, r;
	void f(long i)
	{
		if (used[i]) return;
		if (par[i].empty)
		{
			used[i] = true;
			l ~= i;
			foreach (j; chi[i].keys)
			{
				par[j].remove(i);
				if (par[j].empty)
					f(j);
			}
		}
		else if (chi[i].empty)
		{
			used[i] = true;
			r ~= i;
			foreach (j; par[i].keys)
			{
				chi[j].remove(i);
				if (chi[j].empty)
					f(j);
			}
		}
	}
	foreach (i; 0..N)
	{
		f(i);
		debug writeln("i:", i, " ", l, r);
		debug writeln(par);
		debug writeln(chi);
	}
	foreach (i; 0..N)
	{
		f(i);
	}
	
	long[] ans;
	foreach (e; l)
		ans ~= e;
	foreach_reverse (e; r)
		ans ~= e;

	bool isLoop;
	foreach (i; 0..N)
	{
		if (!used[i])
		{
			isLoop = true;
			ans ~= i;
		}
	}

	if (isLoop)
		writeln(ans.length);
	else
		writeln(ans.length-1);

	foreach (i; 0..ans.length-1)
		writeln(ans[i]+1, " ", ans[i+1]+1);
	if (isLoop)
		writeln(ans[$-1]+1, " ", ans[0]+1);

	stdout.flush;
	debug readln;
}