#include <bits/stdc++.h>

using namespace std;

const int N = 1005;

int ed, vis[N];
vector< pair<int, int> > G[N];
vector<int> z;

void dfs(int x)
{
    int v, w;
    while (G[x].size()) tie(v, w) = G[x].back(), G[x].pop_back(), dfs(v), w && (z.push_back(w), 0);
}

vector< pair<int, int> > tp;

void add()
{
    tp.push_back(make_pair(z[0], ed));
    for (int i = 1; i < z.size(); ++i) tp.push_back(make_pair(z[i], z[i - 1]));
    tp.push_back(make_pair(ed, z.back()));
    return;
}

signed main()
{
    int n, m;
    scanf("%d%d", &n, &m);
    ed = n * m + 1;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1, x; j <= m; ++j) {
            scanf("%d", &x);
            if (vis[x]++) G[x].push_back(make_pair(m + i, (i - 1) * m + j));
        }
        for (int j = 1; j <= m; vis[j++] = 0) if (!vis[j])
            G[m + i].push_back(make_pair(j, 0));
    }
    for (int i = 1; i <= m + n; ++i) vis[i] = 0;
    for (int i = 1; i <= m; ++i) {
        if (G[i].size() && !vis[i]) {
            z.clear();
            dfs(i);
            add();
        }
    }
    printf("%d\n", tp.size());
    for (auto [x, y] : tp) printf("%d %d\n", x, y);
    return 0;
}