#include <bits/stdc++.h>
using namespace std;
const int N = 100000 + 1067;
int res, f[N], c[N], dist[10000 + 1067], avail[N], cur, s, t, n, m, lay[N],
    u[N], v[N], edges, val[N], q[N], dem, now[N];
int oo = 1000000000;
vector<int> to[N];
bool bfs() {
  for (int i = 0; i <= n + m + 1; i++) dist[i] = 0;
  int l, r;
  l = 0;
  r = 1;
  q[1] = s;
  dist[s] = 1;
  while (l < r) {
    ++l;
    int x = q[l];
    for (int i = 0; i <= (int)to[x].size() - 1; i++) {
      int edge = to[x][i];
      if (f[edge] < c[edge] && (!dist[v[edge]])) {
        dist[v[edge]] = dist[x] + 1;
        ++r;
        q[r] = v[edge];
      }
    }
  }
  return dist[t] != 0;
}
int dfs(int x, int mn) {
  if (x == t) return mn;
  if (avail[x] != cur)
    avail[x] = cur;
  else
    return 0;
  for (int i = now[x]; i <= (int)to[x].size() - 1; i++) {
    now[x] = i;
    int edge = to[x][i];
    if (f[edge] < c[edge]) {
      if (avail[v[edge]] != cur && dist[v[edge]] == dist[x] + 1) {
        if (int x = dfs(v[edge], min(c[edge] - f[edge], mn))) {
          f[edge] += x;
          f[lay[edge]] -= x;
          return x;
        }
      }
    }
  }
  return 0;
}
void dinitz() {
  res = 0;
  while (bfs()) {
    for (int i = 0; i <= n + m + 1; i++) now[i] = 0;
    while (true) {
      ++cur;
      int x = dfs(s, oo);
      if (x == 0) break;
      res += x;
    }
  }
}
bool check(int x) {
  for (int i = 1; i <= edges; i++) f[i] = f[lay[i]] = 0;
  for (int i = 1; i <= n; i++) c[i] = x;
  dinitz();
  if (res >= m)
    return true;
  else
    return false;
}
void print(int x) {
  for (int i = 1; i <= edges; i++) f[i] = f[lay[i]] = 0;
  for (int i = 1; i <= n; i++) c[i] = x;
  dinitz();
  cout << x << endl;
  for (int i = n + m + 1; i <= n + m * 3; i++)
    if (f[i] == 1) cout << u[i] << " " << val[i] << endl;
}
int bs(int l, int r) {
  while (l < r) {
    if (l == r - 1)
      if (check(l))
        return l;
      else
        return r;
    int mid = (l + r) / 2;
    if (check(mid))
      r = mid;
    else
      l = mid + 1;
  }
  return r;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  s = 0;
  t = n + m + 1;
  for (int i = 1; i <= n; i++) ++edges, u[edges] = 0, v[edges] = i;
  for (int i = n + 1; i <= n + m; i++)
    ++edges, u[edges] = i, v[edges] = t, c[edges] = 1;
  ;
  for (int i = n + 1; i <= m + n; i++) {
    int a, b;
    cin >> a >> b;
    ++edges;
    u[edges] = a;
    v[edges] = i;
    c[edges] = 1;
    val[edges] = b;
    ++edges;
    u[edges] = b;
    v[edges] = i;
    c[edges] = 1;
    val[edges] = a;
  }
  for (int i = 1; i <= edges; i++) {
    lay[i] = i + edges;
    lay[i + edges] = i;
    v[edges + i] = u[i];
    to[u[i]].push_back(i);
    to[v[i]].push_back(i + edges);
  }
  print(bs(0, n));
  return 0;
}
