#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }


vector<int> uf;
int root(int u) {
  return (uf[u] < 0) ? u : (uf[u] = root(uf[u]));
}
bool connect(int u, int v) {
  u = root(u);
  v = root(v);
  if (u == v) return false;
  if (uf[u] > uf[v]) swap(u, v);
  uf[u] += uf[v];
  uf[v] = u;
  return true;
}


int N, M;
int A[410][410];

int V;
vector<vector<pair<int, int>>> graph;

vector<pair<int, int>> es;
void dfs(int u) {
  for (; !graph[u].empty(); ) {
    const auto e = graph[u].back();
    graph[u].pop_back();
    dfs(e.first);
    es.push_back(e);
  }
}

int main() {
  freopen("depot.in", "r", stdin);
  freopen("depot.out", "w", stdout);
  
  for (; ~scanf("%d%d", &N, &M); ) {
    for (int u = 0; u < N; ++u) for (int i = 0; i < M; ++i) {
      scanf("%d", &A[u][i]);
      --A[u][i];
    }
    
    int ans = 0;
    V = N + M;
    graph.assign(V, {});
    for (int u = 0; u < N; ++u) {
      vector<int> freq(M, 0);
      for (int i = 0; i < M; ++i) {
        const int a = A[u][i];
        if (++freq[a] > 1) {
          ++ans;
          graph[u].emplace_back(N + a, u * M + i);
        }
      }
      for (int a = 0; a < M; ++a) if (freq[a] == 0) {
        graph[N + a].emplace_back(u, -1);
      }
    }
    
    uf.assign(V, -1);
    for (int u = 0; u < V; ++u) {
      for (const auto &e : graph[u]) {
        connect(u, e.first);
      }
    }
    vector<int> has(V, 0);
    for (int u = 0; u < V; ++u) {
      for (const auto &e : graph[u]) {
        has[root(u)] = 1;
      }
    }
    for (int r = 0; r < V; ++r) if (uf[r] < 0) {
      if (has[r]) {
        ++ans;
      }
    }
    
    printf("%d\n", ans);
    
    auto oper = [&](int pos0, int pos1) -> void {
      printf("%d %d\n", pos0 + 1, pos1 + 1);
    };
    for (int u = 0; u < V; ++u) {
      es.clear();
      dfs(u);
      if (!es.empty()) {
// cerr<<"es = "<<es<<endl;
        int pos = N * M;
        for (const auto &e : es) if (~e.second) {
          oper(e.second, pos);
          pos = e.second;
        }
        oper(N * M, pos);
      }
    }
  }
  return 0;
}