救民于水火

#include <bits/stdc++.h>
using namespace std;
int n, dp[5050][3];
struct cheng {
    int a, b;
} c[5050];
bool cmp(cheng x, cheng y) { return x.a < y.a; }
int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> c[i].a >> c[i].b;
    }
    dp[0][2] = -1;
    sort(c + 1, c + n + 1, cmp);
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < i; j++) {
            if (dp[j][2] < c[i].b) {
                if (dp[j][1] + 1 > dp[i][1]) {
                    dp[i][1] = dp[j][1] + 1;
                    dp[i][2] = c[i].b;
                }
            }
        }
    }
    int ans = -1;
    for (int i = 1; i <= n; i++) {
        ans = max(ans, dp[i][1]);
    }
    cout << ans;
    return 0;
}