#include <stdio.h>
int main()
{
int n,sum=0,k=1;
scanf("%d",&n);
while(k<=n)n-=k,sum+=k*k,k++;
printf("%d\n",sum+=n*k);
return 0;
}
#include <stdio.h>
int main()
{
int i,j,n,sum=0,k=1;
scanf("%d",&n);
for(i=1;i<=141;++i)
for(j=1;j<=i;++k,++j)
{
if(k!=n)sum+=i;
else{printf("%d\n",sum+i);return 0;}
}
}