#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
const int Maxlen=10001;
int a[1000],len,j,n;
int main()
{
memset(a,0,sizeof(a));
len=1;
cin>>n;
for(int i=1;i<=n;i++)
{
a[1]+=i;
for(j=1;j<=len;j++)
{
a[j+1]+=(a[j]/10);
a[j]%=10;
}
while(a[len+1]>0)
{
len++;
a[len+1]+=a[len]/10;
a[len]%=10;
}
}

for(int i=len;i>0;i--)
cout<<a[i];
return 0;
}