class Solution {
public:
    int maxEnvelopes(vector<pair<int, int>>& envelopes) {
        if (envelopes.empty()) return 0;
        sort(envelopes.begin(), envelopes.end());

        vector<int> dp(envelopes.size(), 1);

        for (int i = 1; i < envelopes.size(); ++i) {
            for (int j = 0; j < i; ++j) {
                if (envelopes[j].first < envelopes[i].first &&
                    envelopes[j].second < envelopes[i].second)
                     dp[i] = max(dp[i], dp[j] + 1);
            }
        }

        return *max_element(dp.begin(), dp.end());
    }
};