/**
 * @date    2023-05-20 10:48:58
 * RAmen!
 */
#include<bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pii pair<int, int>
#define ll long long
using namespace std;
int n;
int l[5005], r[5005];
bitset<5005> g[5005];
bitset<5005> vis, cur;
int mat[5005], prv[5005];
bool bfs(int s) {
    queue<int> q; q.push(s); vis.set(); prv[s] = -1;
    while(!q.empty()) {
        int u = q.front(); q.pop(); cur = vis & g[u]; bool f = 0;
        for(int v = cur._Find_first(); v <= n; v = cur._Find_next(v)) {
            vis[v] = 0;
            if(mat[v] > 0) {
                q.push(mat[v]); prv[mat[v]] = u;
            }
            else {
                f = 1; int a = u, b = v;
                while(a != -1) {
                    int tmp = mat[a];
                    mat[a] = b;
                    a = prv[a]; b = tmp;
                }
            }
        }
        if(f) break;
    }
    return mat[s] > 0;
}
int main(){
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
        scanf("%d %d", &l[i], &r[i]);
    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])
                g[j][i] = 1;
    int ans = n * 2;
    for(int i = 1; i <= n; i++)
        if(!mat[i])
            ans -= bfs(i);
    printf("%d\n", ans);
    return 0;
}