#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <stack>

using namespace std;
typedef pair<int, int> PII;
#define x first
#define y second

const int N = 600;
int ans, f[N];
PII a[N];

int main() {
#ifndef ONLINE_JUDGE
    freopen("POJ1548.in", "r", stdin);
#endif
    while (true) {
        memset(f, 0, sizeof f);
        ans = 0;
        int al = 0;
        while (true) {
            int x, y;
            scanf("%d %d", &x, &y);
            if (x == -1) exit(0);
            if (x == 0) break;
            a[al++] = make_pair(x, y);
        }

        sort(a, a + al);

        // LIS
        for (int i = 0; i < al; i++) f[i] = 1; // DP初始化
        for (int i = 0; i < al; i++)
            for (int j = 0; j < i; j++)
                if (a[j].y > a[i].y) f[i] = max(f[i], f[j] + 1);
        // Dilworth
        for (int i = 0; i < al; i++) ans = max(ans, f[i]);
        printf("%d\n", ans);
    }
    return 0;
}