/* @author: Praveen Dhinwa */
#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);(i)++)
#define rep1(i,a,b) for(int (i)=(a);(i)<=(int)(b);(i)++)
#define fore(c,itr) for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)
 
using namespace std;
 
const int N = (int) 1e5 + 5;
vector <int> g[N];
set <pair <int, int> > blocked;
 
int dfs (int v) {
  vector <int> adj;
  for (int i = 0; i < g[v].size(); i++) if (blocked.find (make_pair (g[v][i], v)) == blocked.end()) adj.push_back(g[v][i]);
  for (int i = 0; i < adj.size(); i++) {
    int u = adj[i];
    blocked.insert (make_pair (u, v));
    blocked.insert (make_pair (v, u));
  }
  vector <int> unpaired;
  for (int i = 0; i < adj.size(); i++) {
    int u = adj[i];
    int w = dfs (u);
    if (w != 0) unpaired.push_back(w);
  }
  cout << unpaired.size() << endl;
  for (int i = 0; i + 1 < unpaired.size(); i += 2) {
    int u = unpaired[i], w = unpaired[i + 1];
    printf ("%d %d %d\n", u, v, w);
  }
  if (unpaired.size() % 2 == 1) {
    return unpaired[unpaired.size() - 1];
  } else return 0;
}
 
int main() {
  int n, m;
  scanf ("%d %d", &n, &m);
  for (int i = 0; i < m; i++) {
    int u, v;
    scanf ("%d %d", &u, &v);
    g[u].push_back (v);
    g[v].push_back (u);
  }
  if (m & 1) cout << -1 << endl;
  else dfs (1);
  return 0;
}
 

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