一点都不详细版（你！又在给我差评！）😕

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int day, nowday, money;
    cin >> day;
    nowday = money = 0;
    for (int i = 1;; i++)
    {
        for (int j = 1; j <= i; j++)
        {
            money += i;
            nowday += 1;
            if (nowday == day)
                break;
        }
        if (nowday == day)
            break;
    }
    cout << money;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int k;
int ans;
int now;
int pre;
signed main()
{
	cin>>k;
	pre=1;
	for(int i=1;i<=k;i++)
	{
		now++;
		ans+=pre;
		if(now==pre)
		{
			pre++;
			now=0;
		}
	}
	cout<<ans;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int k;
	cin>>k;
	int ans=0;
	int a;//当前属于哪一部分（1,2,3）
	int b;//属于当前部分的第几天
	a=1;
	b=1; 
	for(int i=1;i<=k;i++){	
		ans+=a;  
		b++;
		if(b>a)
		{
			a++;
			b=1;
		}
	}
	cout<<ans<<"\n"; 
	return 0;
}

每一天一块一块发

（压行版）

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