// sis puella oier
#include <bits/stdc++.h>
using namespace std;
// #define int long long
// typedef long long ll;
int read(){
    int xx = 0, f = 1; char ch = getchar();
    for (;!isdigit(ch); ch = getchar())
        f = (ch == '-' ? -1 : 1);
    for (; isdigit(ch); ch = getchar())
        xx = (xx << 3) + (xx << 1) + ch - '0';
    return xx * f;
}
const int N = 10002, inf = 1e9 + 7;
int tot, s, t;
bitset <N> e[N];
int d[N];
bool bfs(){
    for (int i = 1; i <= tot; ++i)d[i] = -1;
    d[s] = 0; queue <int> q; q.push(s);
    int x;
    while(!q.empty()){
        x = q.front(); q.pop();
        for (int v = e[x]._Find_first(); v <= tot; v = e[x]._Find_next(v)){
            if (d[v] == -1 && e[x][v] > 0){
                d[v] = d[x] + 1;
                if (v == t)return true;
                q.push(v);
            }
        }
    }
    return false;
}
int dfs(int x, int lim){
    if (x == t)return lim;
    int flow = 0, ret;
    for (int v = e[x]._Find_first(); v <= tot; v = e[x]._Find_next(v)){
        if (d[v] == d[x] + 1 && e[x][v] > 0){
            ret = dfs(v, min(lim - flow, 1));
            if (ret <= 0)d[v] = -1;
            e[x][v] = 0, e[v][x] = 1, flow += ret;
        }
    }
    return flow;
}
int dinic(){
    int ret = 0, flow;
    while(bfs())while(flow = dfs(s, inf))ret += flow;
    return ret;
}
int n, l[N], r[N], fl[N];
signed main(){
    n = read(), tot = n + n + 2, s = n + n + 1, t = n + n + 2;
    for (int i = 1; i <= n; ++i)l[i] = read(), r[i] = read(),
    fl[l[i]] = -1, fl[r[i]] = 1;
    for (int i = 1; i <= n; ++i)for (int j = i; j <= n; ++j)
        if (l[i] < l[j] && l[j] < r[i] && r[i] < r[j])
            e[l[j]][r[i]] = 1;
    for (int i = 1; i <= n + n; ++i)if (fl[i] == -1)e[s][i] = 1;
    for (int j = 1; j <= n + n; ++j)if (fl[j] == 1)e[j][t] = 1;
    int ans = n + n - dinic();
    printf("%d\n", ans);
    return 0;
}