#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
#define lg long long
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
const lg N = 2e5+5;
vector<lg> adj[N];
lg in[N], state[N];
int main()
{
fastio;
lg n, m;
cin >> n >> m;
for(int i = 0; i < m; i++)
{
lg u, v;
cin >> u >> v;
adj[u].push_back(v);
in[v]++;
}
queue<lg> q;
lg z = 0;
for(int i = 1; i <= n; i++)
{
if(in[i]) continue;
z++;
q.push(i);
}
while(q.size())
{
lg u = q.front();
q.pop();
for(auto it : adj[u])
{
state[u] = true;
in[it]--;
if(!in[it])
{
q.push(it);
state[it] = false;
z++;
}
}
}
if(z < n)
{
cout << "-1\n";
return 0;
}
cout << n << '\n';
for(int i = 1; i <= n; i++)
{
cout << i << ' ' << state[i] << '\n';
}
return 0;
}
