#include <bits/stdc++.h>
using namespace std;
#define sz(x) (int)x.size()
#define all(x) x.begin() , x.end()
void solve(){
int n,m;
cin >> n >> m;
vector < int > ingraph[n] , outgraph[n];
int indegree[n]={0} , outdegree[n]={0};
for(int i = 0;i<m;i++){
int a,b;
cin >> a >> b;
a-- , b--;
ingraph[a].push_back(b);
outgraph[b].push_back(a);
indegree[a]++;
outdegree[b]++;
}
queue < int > q;
for(int i = 0;i<n;i++){
if((indegree[i]==0) or (outdegree[i]==0)){
q.push(i);
}
}
int vis[n]={0};
vector < pair < int , int > > ans;
auto remove_edge = [&](int a , int b){
indegree[a]--;
outdegree[b]--;
};
while(sz(q)){
int tmp = q.front();
q.pop();
if(vis[tmp])continue;
vis[tmp] = 1;
ans.push_back({tmp , sz(ingraph[tmp]) > 0});
for(auto itr : ingraph[tmp]){
remove_edge(tmp , itr);
}
for(auto itr : outgraph[tmp]){
remove_edge(itr , tmp);
}
for(auto itr : ingraph[tmp]){
if(vis[itr] == 0 and ((indegree[itr]==0) or (outdegree[itr]==0))){
q.push(itr);
}
}
for(auto itr : outgraph[tmp]){
if(vis[itr] == 0 and ((indegree[itr]==0) or (outdegree[itr]==0))){
q.push(itr);
}
}
}
for(int i = 0;i<n;i++){
if(vis[i] == 0){
cout << -1 << endl;
return;
}
}
reverse(all(ans));
cout << sz(ans) << endl;
for(auto itr : ans)cout << itr.first+1 << " " << itr.second << '\n';
cout << endl;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);
int testcase=1;//cin >> testcase;
while(testcase--)solve();
cerr << 1000.0 * clock() / CLOCKS_PER_SEC << " ms" << endl;
}
