#include <bits/stdc++.h>
using namespace std;

int a[1005], b[1005];
bool s[1005] = {false};

int main()
{
    int n, sum = 0, maxsum = -1;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i] >> b[i];
    }
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= n; j++)
        {
            if (j != i)
            {
                for (int k = a[i]; k <= b[i]; k++)
                {
                    s[k] = true;
                }
            }
        }
        for (int j = 0; j <= 1000; j++)
        {
            sum += s[j];
        }
        maxsum = max(maxsum, sum);
        for (int j = 0; j <= 1000; j++)
        {
            s[j] = 0;
        }
    }
    cout << maxsum << endl;
    return 0;
}

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再此先谢过好心大佬帮忙