// 有点怀疑这代码的正确性

#include<bits/stdc++.h>
#define int long long

using namespace std;

inline int read() {
    int f = 1;
    int res = 0;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        res = res * 10 + ch - '0';
        ch = getchar();
    }
    return res * f;
}

const int maxn = 410;

int n, m;
vector < int > pos[maxn][maxn];//用 vector 实现，不然会 MLE
int tot[maxn][maxn];

struct node {
    int from;
    int to;
    int next;
}
edge[maxn * maxn * 2];
int head[maxn << 1];
int cnt;

void add(int u, int v) {
    edge[++cnt].to = v;
    edge[cnt].from = u;
    edge[cnt].next = head[u];
    head[u] = cnt;
}

int que[maxn * maxn * 2], tag;
bool vis[maxn * maxn * 2];

void dfs(int now) {
    for (int i = head[now]; i; i = edge[i].next) {
        if (vis[i])
            continue;
        int v = edge[i].to;
        vis[i] = true;
        dfs(v);
        que[++tag] = i;
    }
}

struct ANS {
    int x;
    int y;
}
ans[maxn * maxn + maxn];
int len;

signed main() {
    n = read(), m = read();
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            int x = read();
            ++tot[i][x];
            pos[i][x].push_back((i - 1) * m + j);
        }
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            for (int k = 1; k < tot[i][j]; k++) {
                add(i, j + n);
            }
            if (tot[i][j] < 1)
                add(j + n, i);
        }
    }
    for (int i = n + 1; i <= n + m; i++) {
        tag = 0;
        dfs(i);
        int to = n * m + 1;
        for (int i = 1; i <= tag; i++) {
            int u = edge[que[i]].from;
            int v = edge[que[i]].to;
            if (u <= n) {
                ans[++len].x = pos[u][v - n][--tot[u][v - n]];
                ans[len].y = to;
                to = ans[len].x;
            }
        }
        if (tag) {
            ans[++len].x = n * m + 1;
            ans[len].y = to;
        }
    }
    printf("%lld\n", len);
    for (int i = 1; i <= len; i++) {
        printf("%lld %lld\n", ans[i].x, ans[i].y);
    }
    return 0;
}