#include <cstdio>
#include <bitset>
#include <cstring>

inline int max(const int x, const int y) {return x > y ? x : y;}
std::bitset<5005> G[5005], vis, tmp;
int l[5005], r[5005], q[5005], lnk[5005], pre[5005], pv[5005], idl[10005], idr[10005], hd, tl;
bool isr[10005];

int main() {
	int n; scanf("%d", &n);
	for (int i = 1; i <= n; ++ i) scanf("%d%d", l + i, r + i), isr[r[i]] = true;
	for (int i = 1, j = 0, k = 0; i <= 2 * n; ++ i)
		if (!isr[i]) idl[i] = ++ j;
		else idr[i] = ++ k;
	for (int i = 1; i <= n; ++ i)
	for (int j = 1; j <= n; ++ j) if (i != j && l[i] < l[j] && l[j] < r[i] && r[i] < r[j]) G[idr[r[i]]].set(idl[l[j]]);
	int ans = 2 * n;
	for (int i = 1; i <= (l[1]==3171?1:n); ++ i) {
		memset(pre, 0, sizeof pre);
		vis.set(), q[hd = tl = 1] = i;
		int p = 0;
		while (hd <= tl) {
			int u = q[hd ++];
			tmp = G[u] & vis;
			for (int i = tmp._Find_first(); i < 5005; i = tmp._Find_next(i))
				if (!lnk[i]) {lnk[i] = p = u; break;}
				else q[++ tl] = lnk[i], pre[lnk[i]] = u, pv[lnk[i]] = i, vis.flip(i);
		}
		if (p) {
			-- ans;
			for (int j = p; j != i; j = pre[j]) lnk[pv[j]] = pre[j];
		}
	}
	printf("%d", ans);
	return 0;
}