#include<bits/stdc++.h>
using namespace std;
namespace my_std{
	#define ll long long
	#define bl bool
	ll my_pow(ll a,ll b,ll mod){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res=(res*a)%mod;
			a=(a*a)%mod;
			b>>=1;
		}
		return res;
	}
	ll qpow(ll a,ll b){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res*=a;
			a*=a;
			b>>=1;
		}
		return res;
	}
	#define db double
	#define pf printf
	#define pc putchar
	#define fr(i,x,y) for(register ll i=(x);i<=(y);i++)
	#define pfr(i,x,y) for(register ll i=(x);i>=(y);i--)
	#define go(u) for(ll i=head[u];i;i=e[i].nxt)
	#define enter pc('\n')
	#define space pc(' ')
	#define fir first
	#define sec second
	#define MP make_pair
	#define il inline
	#define inf 8e18
	#define random(x) rand()*rand()%(x)
	#define inv(a,mod) my_pow((a),(mod-2),(mod))
	il ll read(){
		ll sum=0,f=1;
		char ch=0;
		while(!isdigit(ch)){
			if(ch=='-') f=-1;
			ch=getchar();
		}
		while(isdigit(ch)){
			sum=sum*10+(ch^48);
			ch=getchar();
		}
		return sum*f;
	}
	il void write(ll x){
		if(x<0){
			x=-x;
			pc('-');
		}
		if(x>9) write(x/10);
		pc(x%10+'0');
	}
	il void writeln(ll x){
		write(x);
		enter;
	}
	il void writesp(ll x){
		write(x);
		space;
	}
}
using namespace my_std;
vector<ll> ans;
ll n,m,a[440],head[880],cnt=0;
bl ck[440],pd[880];
struct node{
	ll nxt,to,w;
}e[200020];
void add(ll u,ll v,ll ww){
	e[++cnt].nxt=head[u];
	e[cnt].to=v;
	e[cnt].w=ww;
	head[u]=cnt;
}
void dfs(ll u){
	pd[u]=1;
	for(ll i=head[u];i;i=head[u]){
		head[u]=e[i].nxt;
		ll v=e[i].to;
		dfs(v);
		if(e[i].w) ans.push_back(e[i].w);
	}
}
int main(){
	n=read();
	m=read();
	fr(i,1,n){
		fr(j,1,m){
			a[j]=read();
			if(ck[a[j]]) add(i,n+a[j],(i-1)*m+j);
			ck[a[j]]=1;
		}
		fr(j,1,m){
			if(!ck[j]) add(n+j,i,0);
			ck[j]=0;
		}
	}
	ans.push_back(n*m+1);
	fr(i,1,n){
		if(head[i]){
//			while(pd[i]);
			dfs(i);
			ans.push_back(n*m+1);
		}
	}
	writeln((ll)ans.size()-1);
	fr(i,1,(ll)ans.size()-1) pf("%lld %lld\n",ans[i],ans[i-1]);
}