#include <bits/stdc++.h>

using namespace std; const int maxn = 2e5 + 5, maxm = 2e6 + 5;

int N, M, len;

int a[maxm];

vector<int> G[maxn];

int ct[maxn];

int b[maxm], c;

void DFS(int u)
{
    while (G[u].size())
    {
        int v = G[u].back();
        G[u].pop_back();
        DFS(v);
        // cerr << u << ' ' << v << endl;
    }
    b[c++] = u;
}

pair<int, int> zu[maxm]; int tt;

inline void Swap(int x, int y)
{
    swap(a[x], a[y]);
    assert(tt + 1 < maxm);
    zu[++tt] = { x, y };
}

inline int find(int st, int j)
{
    st -= M;
    st = (st - 1) * M + 1;
    for (int i = 0; i < M; i++) if (a[st + i] == j) return st + i;
    // assert(0);
}

int main()
{
    scanf("%d%d", &N, &M), len = N * M;
    for (int i = 1; i <= len; i++) scanf("%d", a + i);
    for (int i = 1, st = 1; i <= N; i++, st += M)
    {
        memset(ct, 0, sizeof ct);
        for (int j = 0; j < M; j++) ct[a[st + j]]++; //, cerr << a[st + j] << endl;
        for (int j = 1; j <= M; j++)
        {
            if (ct[j] == 0) G[j].push_back(i + M); //, cerr << j << ' ' << i + M << endl;
            else
            {
                for (int k = 1; k < ct[j]; k++) G[i + M].push_back(j); //, cerr << i + M << ' ' << j << endl;
            }
        }
    }
    // cerr << "!" << endl;
    for (int st = 1; st <= M; st++)
    {
        c = 0;
        DFS(st);
        // for (int j = 0; j < c; j++) cerr << b[j] << ' '; cerr << endl;
        c--;
        if (!c) continue;
        // assert(c % 2 == 0);
        // for (int j = 1; j <= c; j++) assert((b[j] > M) == (j % 2 == 1));
        int x = find(b[1], b[c]);
        Swap(x, len + 1);
        for (int i = 3; i < c; i += 2)
        {
            int y = find(b[i], b[i - 1]);
            Swap(y, x);
            x = y;
        }
        Swap(len + 1, x);
    }
    printf("%d\n", tt);
    for (int i = 1; i <= tt; i++) printf("%d %d\n", zu[i].first, zu[i].second);
    return 0;
}