ge

#include <bits/stdc++.h>
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define reset(x) memset(x, 0,sizeof(x))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define N 105
#define remain(x) if (x > MOD) x -= MOD
#define ii pair<int, int>
#define iiii pair< ii , ii >
#define viiii vector< iiii >
#define vi vector<int>
#define vii vector< ii >
#define bit(x, i) (((x) >> (i)) & 1)
#define Task "grab"
#define int long long

using namespace std;

typedef long double ld;
const int inf = 1e10;
const int minf = -1e10;

int n;
int a[N][N];
int dp[N][N];
ii trace[N][N];
int ic, jc;

void readfile()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    if (fopen(Task".inp","r"))
    {
        freopen(Task".inp","r",stdin);
        freopen(Task".out","w",stdout);
    }
    cin >> n;
    memset(a, 0, sizeof a);
    int x, y;
    while (cin >> x >> y)
    {
        a[x][y] = 1;
    }
}

void traceback()
{
    stack<ii> st;
    ii s = ii(ic,jc);
    while (s != ii(0,0))
    {
        st.push(s);
        s = trace[s.fi][s.se];
    }
    while (st.size())
    {
        cout << st.top().fi << ' ' << st.top().se << endl;
        st.pop();
    }
}

void proc()
{
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=n; j++)
        {
            if (a[i][j]==0) dp[i][j] = 0;
            else{
                for(int u = 0; u < i; u++)
                {
                    for(int v=0; v < j; v++)
                    {
                        if (dp[i][j] < dp[u][v] + 1)
                        {
                            dp[i][j] = dp[u][v]+1;
                            trace[i][j] = ii(u,v);
                        }
                    }
                }
            }
        }
    }
    int ans = 0;
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=n; j++)
        {
            if (dp[i][j] > ans)
            {
                ans = dp[i][j];
                ic = i;
                jc = j;
            }
        }
    }
    cout << ans << endl;
    traceback();
}

signed main()
{
    readfile();
    proc();
    return 0;
}