#include <bits/stdc++.h>
#define pb emplace_back
#define fst first
#define scd second
#define mkp make_pair
#define mems(a, x) memset((a), (x), sizeof(a))

using namespace std;
typedef long long ll;
typedef double db;
typedef unsigned long long ull;
typedef long double ldb;
typedef pair<ll, ll> pii;

const int maxn = 200100;
const int N = 980;

int n, a[maxn], f[maxn][999];

inline void upd(int l, int r, int x) {
	f[r][x] = l;
	for (int i = x - 1; ~i; --i) {
		if (f[r][i] < l) {
			f[r][i] = l;
		} else {
			break;
		}
	}
}

inline int query(int l, int r) {
	if (l >= r) {
		return 0;
	}
	for (int i = 0;; ++i) {
		if (f[r][i] < l) {
			return i - 1;
		}
	}
	return 0;
}

void solve() {
	scanf("%d", &n);
	for (int _ = 0, l, r; _ < n; ++_) {
		scanf("%d%d", &l, &r);
		a[r] = l;
	}
	f[1][0] = 1;
	for (int i = 2; i <= n * 2; ++i) {
		for (int j = 0; j <= N; ++j) {
			f[i][j] = f[i - 1][j];
		}
		f[i][0] = i;
		if (a[i]) {
			int x = query(a[i] + 1, i - 1) + 1, k = a[i] - 1;
			upd(a[i], i, x);
			for (int j = 0; j <= N && f[k][j]; ++j) {
				upd(f[k][j], i, j + x);
			}
		}
	}
	printf("%d\n", query(1, n * 2));
}

int main() {
	int T = 1;
	// scanf("%d", &T);
	while (T--) {
		solve();
	}
	return 0;
}