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#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
    short int n, n1, nn, max;
    cin >> n >> n1;
    short int arr[n - 2][2];
    for (int i = 0; i < n - 2; i++)
        for (int j = 0; j < 2; j++)
            cin >> arr[i][j];
    cin >> nn;
    short int maxes[n];
    maxes[0] = n1;
    for (int i = 1; i < n - 1; i++)
        maxes[i] = maxes[i - 1] + arr[i - 1][1] - arr[i - 1][0];
    maxes[n - 1] = maxes[n - 2] - nn;
    max = n1;
    for (int i = 1; i < n; i++)
        if (maxes[i] > max)
            max = maxes[i];
    cout << max;
    return 0;
}

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