#include <bits/stdc++.h>
using namespace std;

constexpr int M = 5010;

int n, l[M], r[M];

bitset<M> vis, e[M];
int pl[M], pr[M], pre[M];
vector<int> vl, vr;

inline bool bfs(int n) {
    queue<int> q;
    q.push(n), vis.set();
    while (!q.empty()) {
        int p = q.front();
        q.pop();
        auto nw = vis & e[p];
        for (int i = nw._Find_first(); i <= n; i = nw._Find_next(i)) {
            vis.reset(i), pre[i] = p;
            if (!pr[i]) {
                while (i) pr[i] = pre[i], swap(i, pl[pre[i]]);
                return true;
            }
            q.push(pr[i]);
        }
    }
    return false;
}
inline int match() {
    int ans = 0;
    for (int i = 1; i <= n; i++) ans += bfs(i);
    return ans;
}

int main() {
    assert(scanf("%d", &n));
    for (int i = 1; i <= n; i++)
        assert(scanf("%d%d", l + i, r + i)), vl.push_back(l[i]), vr.push_back(r[i]);
    auto mUnique = [](vector<int> &v) {
        sort(v.begin(), v.end());
        v.erase(unique(v.begin(), v.end()), v.end());
    };
    mUnique(vl), mUnique(vr);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (l[i] < l[j] && l[j] < r[i] && r[i] < r[j]) {
                int pl = lower_bound(vl.begin(), vl.end(), l[j]) - vl.begin() + 1;
                int pr = lower_bound(vr.begin(), vr.end(), r[i]) - vr.begin() + 1;
                e[pl][pr] = 1;
            }
    printf("%d\n", 2 * n - match());
    return 0;
}