还是不明白为什么WA

#include <iostream>
using namespace std;
const int MAXN = 100;
int main()
{
    int n,s = 0;
    cin >> n;
    int a[MAXN];
    int d;
    cin >> d;
    for (int i = n;i >= 1;i--)
        {
            a[i] = d % 10;
            d = d / 10;
        }
    while (n > 0)
        {
            n = n - 3;
            s++;
        }
    for (int i = 1;i <= s;i++)
        {
            if (i != s)
                {
                    cout << a[2 * i - 1] << a[2 * i] << a[2 * i + 1] << "-";
                }
                else
                    {
                        if (n >= 0)
                            {
                                cout << a[2 * i] << a[2 * i + 1] << a[2 * i + 2];
                            }
                            else
                                {
                                    cout << a[2 * i] << a[2 * i + 1];
                                }
                    }
        }
}

我貌似不存在有多大问题啊【困惑脸】