代码超时啦～～ 64分看起来超的不少～

#include<cstdio>
int main()
{
    long long int n;
    long long int line;
    long long int line_up=1;
    long long int number=0;
    long long int i;

    scanf("%lld",&n);
    if (n<=3){
        printf("0");
    }
   
    else if(n>3)
    {
        for ( line = n-3; line >= 1; line--)
        {
            for ( i = line_up; i <= line*line_up; i=i+line_up)
            {
                number=number+i;
            }
            line_up++;
        }
        printf("%lld\n",number);
    }
    return 0;
}