#include <bits/stdc++.h>

using namespace std;

const int N = 5005;

int n;
pair<int, int> a[N];
bitset<N << 1> g[N << 1];
int s, t;
int dep[N << 1];

bool bfs()
{
    memset(dep, 0, sizeof(dep));
    queue<int> que;
    dep[s] = 1, que.push(s);
    while(!que.empty())
    {
        int u = que.front(); que.pop();
        for(auto v = g[u]._Find_first(); v <= t; v = g[u]._Find_next(v))
            if(!dep[v]) dep[v] = dep[u] + 1, que.push(v);
    }
    return dep[t];
}

int dfs(int u, int in)
{
    if(u == t || !in) return in;
    int out = 0;
    for(auto v  = g[u]._Find_first(); v <= t; v = g[u]._Find_next(v))
    {
        if(dep[v] != dep[u] + 1) continue;
        int f = dfs(v, min(in, 1));
        if(f) g[u][v] = 0, g[v][u] = 1;
        in -= f, out += f;
        if(!in) break;
    }
    return out;
}

int dinic()
{
    int res = 0;
    while(bfs()) res += dfs(s, 1e9);
    return res;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);

    cin >> n; s = 2 * n + 1, t = s + 1;
    for(int i = 1; i <= n; i++) cin >> a[i].first >> a[i].second;
    sort(a + 1, a + n + 1);
    for(int i = 1; i <= n; i++)
        for(int j = i + 1; j <= n; j++)
            if(a[j].first < a[i].second && a[i].second < a[j].second)
                g[j][n + 1] = 1;
    for(int i = 1; i <= n; i++) g[s][i] = 1, g[n + i][t] = 1;

    cout << 2 * n - dinic() << '\n';
    return 0;
}