wa了第二个测试点，求助ing

#include <iostream>
using namespace std;

int ans[5005][1000] = {{0},{1},{2}} , len=0;
void fun(int n)
{
    int i , a , b , c;
    for(i=0;i<=len;i++){
        a = ans[n-1][i] , b = ans[n-2][i] , c = ans[n][i];
        if(a+b+c>9)   ans[n][i] = a+b+c-10 , ans[n][i+1]++;
        else    ans[n][i] = a+b+c;
    }
    if(ans[n][len+1])   len++;
}
int main()
{
    int n ;
    cin >> n ;
    for(int i=3;i<=n;i++)
        fun(i);
    for(int i=len;i>=0;i--)
        cout << ans[n][i];
    return 0 ;
}