#include<bits/stdc++.h>
#define File(name) freopen(#name".in", "r", stdin); freopen(#name".out", "w", stdout);
using namespace std;
using ll = long long;
using ull = unsigned long long;
template<typename T>
inline T read(){
    T n = 0; int f = 1; char ch = getchar();
    while(!isdigit(ch)){
        if(ch == '-') f = -1;
        ch = getchar();
    }
    while(isdigit(ch)){
        n = n * 10 + ch - '0';
        ch = getchar();
    }
    return f * n;
}
template<typename T>
void write(T n){
    if(n/10) write(n/10);
    putchar(n%10+'0');
}
void input() {}
template<typename Type, typename... Types>
void input(Type &arg, Types&... args){
    arg = read<Type>();
    input(args...);
}
namespace Main{
    const int N = 405;
    int n, m;
    vector<int> pos[N][N], res;
    vector<int> g[N<<1];
    vector<pair<int, int>> ans;
    void dfs(int u){
        while(!g[u].empty()){
            int v = g[u].back(); g[u].pop_back();
            dfs(v);
            res.push_back(u);
        }
    }
    void Main(){
        input(n, m);
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                int x;
                input(x);
                pos[i][x - 1].push_back(i * m + j + 1);
            }
        }
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(pos[i][j].size() == 0) g[n + j].push_back(i);
                else for(int k = 1; k < pos[i][j].size(); k++) g[i].push_back(n + j);
            }
        }
        for(int i = 0; i < n; i++){
            res.clear();
            dfs(i);
            assert(res.size() % 2 == 0);
            int lst = n * m + 1;
            for(int i = 0; i < res.size(); i += 2){
                ans.emplace_back(pos[res[i + 1]][res[i] - n].back(), lst);
                lst = pos[res[i + 1]][res[i] - n].back();
                pos[res[i + 1]][res[i] - n].pop_back();
            }
            if(lst != n * m + 1) ans.emplace_back(n * m + 1, lst);
        }
        write(ans.size()); puts("");
        for(pair<int, int> x: ans) write(x.first), putchar(' '), write(x.second), puts("");
        return;
    }
} // namespace
int main(){
#ifdef Liuxizai
    freopen("in", "r", stdin);
    freopen("out", "w", stdout);
#endif // Liuxizai
    Main::Main();
    return 0;
}