#include <stdlib.h>
#include <math.h>
#include <stdio.h>
void erostane(bool *a,unsigned long n)
{

   for(int i=2;i<=n;++i)
   {
       a[i] = 1;
   }
   for(int i=2;i<=sqrt(n);++i)
    if(a[i])
        for(int j=i;j<=n/i;++j)
            a[j*i] = 0;

}

int main()
{
    unsigned long n,sum;
    bool *v;
    freopen("fractii.in", "rt", stdin);
    freopen("fractii.out", "wt", stdout);

    scanf("%lu", &n);
    sum = 2*n;
    v = (bool *)malloc(n*sizeof(bool));
    erostane(v,n);
    //printf("%d", v[0]);
    for(long i=2;i<n;i++)
        {
            if(v[i])
            sum += i - 1;
        }
   printf("%d", sum);
    return 0;
}