#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <set>
#include <algorithm>
using namespace std;

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

const int N = 1010, M = N * N;

int e[M], h[N], idx, w[M], ne[M];
void add(int a, int b, int c = 0) {
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
}

int st[N], match[N];
int dfs(int u) {
    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (st[v] == 1) continue;
        st[v] = 1;
        if (match[v] == -1 || dfs(match[v])) {
            match[v] = u;
            return 1;
        }
    }
    return 0;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("POJ1548.in", "r", stdin);
#endif
    int a, b;
    while (true) {
        memset(match, -1, sizeof match);
        memset(st, 0, sizeof st);

        memset(h, -1, sizeof h);
        idx = 0;

        vector<PII> vec;
        while (true) {
            cin >> a >> b;
            if (a == 0 && b == 0) break;
            if (a == -1 && b == -1) exit(0);
            vec.push_back(make_pair(a, b));
        }

        sort(vec.begin(), vec.end());

        vector<int> alls; // 存储所有待离散化的值
        for (int i = 0; i < vec.size(); i++)
            for (int j = i + 1; j < vec.size(); j++)
                if (vec[j].y >= vec[i].y) alls.push_back(i), alls.push_back(j);

        // 将所有值排序
        sort(alls.begin(), alls.end());
        // 去掉重复元素
        alls.erase(unique(alls.begin(), alls.end()), alls.end());

        // 重新捋着建边，通过二分查找，找出新的序号，这样就可以使用i<=alls.size()了！
        for (int i = 0; i < vec.size(); i++)
            for (int j = i + 1; j < vec.size(); j++)
                if (vec[j].y >= vec[i].y) {
                    int x = lower_bound(alls.begin(), alls.end(), i) - alls.begin();
                    int y = lower_bound(alls.begin(), alls.end(), j) - alls.begin();
                    add(x, y);
                }

        int res = 0;

        for (int i = 0; i < alls.size(); i++) {
            // 最开始黄海SB的以为二分后，这里可以使用i<idx做为终止条件，其实是SB到家了！idx是边数，是边数，是边数！
            // 不是点数，不是点数，不是点数！
            memset(st, 0, sizeof st);
            if (dfs(i)) res++;
        }

        printf("%d\n", vec.size() - res);
    }
    return 0;
}