虽然函数题但不想用函数（bool那种）

#include <bits/stdc++.h> 
using namespace std;
int main()
{
    int n, sum = 0, x = 1, e = 1;
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        sum += x;
        x += e;
        e++;
    }
    cout << sum;
    return 0;
}//已AC

简单的要S （￣︶￣）↗

#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int main()
{
    int n,a[N];
    cin >> n;
    a[1] = 1;
    for (int i = 2;i <= N;i++)
    {
        a[i] += a[i - 1] + i - 1;
    }
    long long  sum = 0;
    for (int i = 1;i <= n;i++)
    {
        sum += a[i];
    }
    cout << sum;
    return 0;
}

#include <iostream>
using namespace std;
int serie(int n)
{
	if (n == 1 || n == 2)
	{
		return n;
	}
	else
	{
		return n - 1 + serie(n - 1);
	}
}
int main()
{
	int n;
	cin >> n;
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		sum += serie(i);
	}
	cout << sum;
	return 0;
}