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#include<iostream>
using namespace std;
int main()
{
int a,m=1,num=0,u=0;
cin>>a;
for(int i=1;i<=a;0)
{
num++;
for(int i2=1;i2<=num and i<=a;i2++)
{
u+=num;
i++;
}
}
cout<<u;
}