有没有大佬帮忙看一下为什么会 段错误啊

#define _CRT_SECURE_NO_WARNINGS

#include<cstdio>
#include<iostream>

using namespace std;


#define MOD (int)10000 
#define N 2


struct mat
{
    int a[N][N];

    mat()
    {
        for (int i = 0; i < N; ++i)
        {
            for (int j = 0; j < N; ++j)
            {
                a[i][j] = 0;
            }
        }
    }

    void setUnitMat()
    {
        for (int i = 0; i < N; ++i)
            a[i][i] = 1;
    }
};

mat&& matMul(mat& a, mat& b)
{
    mat res;
    for (int i = 0; i < N; ++i)
    {
        for (int j = 0; j < N; ++j)
        {
            for (int k = 0; k < N; ++k)
            {
                res.a[i][j] += (a.a[i][k]  * b.a[k][j]) % MOD;
                res.a[i][j] % MOD;
            }
        }
    }
    return std::move(res);
}

mat&& fastPow(mat q, int n)
{
    mat u;
    u.setUnitMat();
    while (n > 0)
    {
        if (n & 1) u = matMul(u, q);
        q = matMul(q, q);
        n >>= 1;
    }
    return std::move(u);
}

int main(void)
{
    int n;
    mat q;
    q.a[0][0] = q.a[0][1] = q.a[1][0] = 1;
    q.a[1][1] = 0;

    scanf("%d", &n);
    while (n != -1)
    {
        if (n <= 1)
        {
            printf("%d\n", n);
            scanf("%d", &n);
            continue;
        }
        mat res = fastPow(q, n - 1);
        printf("%d\n", res.a[0][0] % MOD);
        scanf("%d", &n);
    }

    return 0;
}