#include <iostream>
#include <cstdio>
#include <cctype>
#include <vector>
#include <cstring>
#include <algorithm>
#include <bitset>
using namespace std;

const int N = 5008;

int n, m;
int l[N], r[N];
bitset<N> g[N], nw, vis;
int pre[N], pl[N], pr[N];
int q[N + N], hd, tl;
int ln[N], rn[N];

bool bfs(int s)
{
    hd = tl = 0;
    q[++tl] = s;
    pre[s] = 0;
    vis.set();
    while (hd < tl) {
        int x = q[++hd];
        nw = vis & g[x];
        for (int i = nw._Find_first(); i <= n; i = nw._Find_next(i)) {
        // for (int i = 1; i <= n; i++) if (nw[i]) {
            vis.reset(i);
            pre[i] = x;
            if (!pr[i]) {
                while (i) {
                    pr[i] = pre[i];
                    swap(i, pl[pre[i]]);
                }
                return 1;
            }
            q[++tl] = pr[i];
        }
    }
    return 0;
}

signed main()
{
    ios::sync_with_stdio(false); cin.tie(0), cout.tie(0);
    cin >> n, m = n + n;
    for (int i = 1; i <= n; i++) {
        cin >> l[i] >> r[i];
        ln[l[i]] = i, rn[r[i]] = i;
    }
    for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) {
        if (l[i] < l[j] && r[i] < r[j] && r[i] > l[j]) {
            g[rn[r[i]]].set(ln[l[j]]);
        }
    }
    int ans = 0;
    for (int i = 1; i <= n; i++) ans += bfs(i);
    cout << m - ans << '\n';
    return 0;
}