#include<cstdio>
#include<vector>
#include<cstring>
using namespace std;
#define N 10001
#define M 6000000
#define F(i,V) for(vector<int>::iterator i=V.begin();i!=V.end();i++)
vector<int> g[N];
int l[N],r[N],u[N],n,m,e,x,y,c=1,i,j,o=-1,t;
char p[M];
inline int A()
{
  	int s=0;
  	for(o++;p[o]>47;o++)
  		s=s*10+p[o]-48;
  	return s;
}
inline void S(int x)
{
    int i,d=x>9999?5:x>999?4:x>99?3:x>9?2:1;
    for(i=d-1;i>=0;x/=10,i--)
        p[t+i]=x%10+48;
    t+=d;
}
inline int P(int n)
{
    if(u[n])
		return 0;
    u[n]=1;
    F(i,g[n])
		if(!r[*i])
		{
        	l[n]=*i,r[*i]=n;
        	return 1;
    	}
    F(i,g[n])
		if(P(r[*i]))
		{
        	l[n]=*i,r[*i]=n;
        	return 1;
    	}
    return 0;
}
int main()
{
    freopen("cuplaj.in","r",stdin),freopen("cuplaj.out","w",stdout),fread(p,1,M,stdin),n=A(),m=A(),e=A();
    while(e--)
        x=A(),y=A(),g[x].push_back(y);
    while(c)
        for(c=0,memset(u,0,sizeof(u)),i=1;i<=n;i++)
			if(!l[i])
            	c|=P(i);
    for(i=1;i<=n;i++)
		j+=(l[i]>0);
    for(S(j),p[t++]=10,i=1;i<=n;i++)
		if(l[i]>0)
        	S(i),p[t++]=32,S(l[i]),p[t++]=10;
    fwrite(p,1,t,stdout);
}