#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define fi first
#define se second
#define pp push_back
#define all(x) (x).begin(), (x).end()
#define Ones(n) __builtin_popcount(n)
#define endl '\n'
#define mem(arrr, xx) memset(arrr,xx,sizeof arrr)
//#define int long long
#define debug(x) cout << (#x) << " = " << x << endl

void Gamal() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
#ifdef Clion
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

int dx[] = {+0, +0, -1, +1, +1, +1, -1, -1};
int dy[] = {-1, +1, +0, +0, +1, -1, +1, -1};

const double EPS = 1e-9;
const ll OO = 0X3F3F3F3F3F3F3F3F;
const int N = 50 + 5, INF = INT_MAX, MOD = 1e9 + 7, LOG = 20;

int dp[N], n;
pii a[N];

bool intersect(vector<int> x) {
    for (int i = 0; i < x.size(); ++i) {
        for (int j = 0; j < x.size(); ++j) {
            if(x[i] >= a[x[j]].fi && x[i] <= a[x[j]].se)continue;
            return false;
        }
    }
    return true;
}

int slv(int i) {
    if (i + 2 >= n)return 0;
    int &ret = dp[i];
    if (~ret)
        return ret;
    ret = slv(i + 1);
    if (intersect({i, i + 1 ,i + 2}))
        ret = max(ret, slv(i + 3) + 1);
    return ret;
}

void solve() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        cin >> a[i].fi >> a[i].se;
    }
    sort(a, a + n);
    mem(dp, -1);
    cout << slv(0) << endl;
}


signed main() {
    Gamal();
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}