C++ :

#include<iostream>
using namespace std;
int main()
{
	int k;
	int i = 0;
	int a = 0,b=0;
	cin >> k;
    while(b<=k)
    {
        ++i;
        a+=i*i;
        b=(i+1)*i/2;
    }
    a=a-(b-k)*i;
	cout << a<<endl;
	return 0;
}

Python :

a=int(input())
if a>=1 and a<=10000:
    coins=0
    days=0
    daystrue=0
    tof=1
    while daystrue<=a:
        days+=1
        for i in range(days):
            if daystrue<a:
                coins+=days
                daystrue+=1
            else:
                tof=0
                break
        if tof==0:
            break
    print(coins)