psychopurp 2018-08-07 20:48:17
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#include<iostream>
using namespace std;
int main()
{
int n,k=0,j=1,t=1;
cin >> n;
for (int i = 1; i <= n; i++)
{
if (i > j)
{
t++;
j += t;
}
k += t;
}
cout << k;
return 0;
}