#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
#define fir first
#define sec second
typedef vector <int> vi;
typedef vector <ll> vl;

#ifdef LCX
#define msg(args...) fprintf(stderr, args)
#else
#define msg(...) void()
#endif

const int maxn = 1e4 + 10;
int n, match[maxn];
pii a[maxn];
bitset <maxn> vis, e[maxn];

int dfs(int u) {
    while (1) {
        int v = (vis & e[u])._Find_first();
        if (v > n * 2) break;
        vis[v] = 0;
        if (!match[v] || dfs(match[v])) {
            match[v] = u;
            return 1;
        }
    }
    return 0;
}

int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) scanf("%d%d", &a[i].fir, &a[i].sec);
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j)
            if (a[i].fir < a[j].fir && a[j].fir < a[i].sec && a[i].sec < a[j].sec)
                e[a[i].sec][a[j].fir] = 1;
    int ans = 0;
    for (int i = 1; i <= n * 2; ++i) vis.set(), vis[i] = 0, ans += dfs(i);
    printf("%d\n", n * 2 - ans);
    return 0;
}