#include <unistd.h>
#define pb emplace_back
using namespace std;

inline char readchar() {
    constexpr int B = 1<<10;
    static char buf[B], *p, *q;
    if(p == q && (q=(p=buf)+read(0, buf, B)) == buf) return -1;
    return *p++;
}
inline int nextint() {
    int x = 0, c = readchar();
    while(c < '0') c = readchar();
    while(c >= '0') x=x*10+(c^'0'), c=readchar();
    return x;
}
inline void writeint(int x) {
    static char stk[20], buf[20];
    char p = 0, q = 0;
    if(!x) stk[p++] = '0';
    while(x) stk[p++] = x%10^'0', x/=10;
    while(p) buf[q++] = stk[--p];
    write(1, buf, q);
}

const int N = 24;

int p[N], l[N], r[N], g[N];
int seed = 7122;
inline int rnd() { return seed = 1LL * seed * 14699 % 1000000007; }
inline void swap(int &a, int &b) {
    int t = a; a = b; b = t;
}
void shuffle(int n) {
    for(int i = 0; i < n; i++) {
        int j = rnd() % (i+1);
        if(j != i) swap(p[i], p[j]);
    }
}
inline int min(int a, int b) { return a < b ? a : b; }
int now[N];
signed main() {
    int n = nextint();
    for(int i = 0; i < n; i++) l[i] = nextint(), r[i] = nextint();
    for(int i = 0; i < n; i++) {
        g[i] = 1 << i;
        for(int j = 0; j < n; j++) {
            if(j == i) continue;
            if((l[i] < l[j] && l[j] < r[i]) ^ (l[i] < r[j] && r[j] < r[i])) {
                g[i] |= 1 << j;
            }
        }
    }
    int ans = n;
    for(int i = 0; i < n; i++) p[i] = i;
    for(int c = 0; c < 50; c++) {
        shuffle(n);
        int it = 0;
        for(int i = 0; i < n; i++) {
            bool found = false;
            for(int j = 0; j < it; j++) {
                int &x = now[j];
                if(~x >> p[i] & 1) {
                    x |= g[p[i]];
                    found = true;
                    break;
                }
            }
            if(!found) now[it++] = g[p[i]];
        }
        ans = min(ans, it);
    }
    writeint(ans);
}