居然出现未知错误？请管理员or众大神来解释……

[codec]#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <algorithm>
using namespace std;
int n,i,j,a[1001][1001];
int main()
{    
    scanf("%d",&n);
    for (i=1;i<=n;i++) for (j=1;j<=i;j++) scanf("%d",&a[i][j]);
    for (i=n-1;i>=1;i--)
    for (j=1;j<=n-1;j++)
    a[i][j]+=max(a[i+1][j],a[i+1][j+1]);
    printf("%d\n",a[1][1]);
    return 0;
}[/codec]