#include<iostream>
#include<cstring>
#include<vector>
#include<bitset>
#include<queue>
#include<algorithm>
using namespace std;
using LL = long long;
const int N = 5000;
bitset<N> g[5005];
int match[5005], pre[5005];

bool bfs(int st){
    queue<int> q;
    q.push(st);
    bitset<N> v;
    v.set();
    memset(pre, -1, sizeof pre);
    while(!q.empty()){
        int t = q.front();
        q.pop();
        auto bs = v & g[t];
        for(auto i = bs._Find_first(); i != bs.size(); i = bs._Find_next(i)){
            pre[i + N] = t;
            if (match[i] != -1){
                v.reset(i);
                pre[match[i]] = i;
                q.push(match[i]);
            }
            else{
                for(auto j = i; ; j = pre[pre[j + N]]){
                    match[j] = pre[j + N];
                    if (pre[j + N] == st) break;
                }
                return true;
            }
        }
    }
    return false;
}

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int n;
    cin >> n;
    vector<pair<int, int> > p(n);
    for(int i = 0; i < n; i++){
        cin >> p[i].first >> p[i].second;
    }
    sort(p.begin(), p.end());
    for(int i = 0; i < n; i++){
        auto [l1, r1] = p[i];
        for(int j = i + 1; j < n; j++){
            auto [l2, r2] = p[j];
            if (r1 > l2 and r1 < r2){
                g[i].set(j);
            }
        }
    }
    memset(match, -1, sizeof match);
    int cnt = 0;
    for(int i = 0; i < n; i++){
        cnt += bfs(i);
    }
    cout << 2 * n - cnt << '\n';

}