#include <fstream>
#include <stdio.h>
using namespace std;
long long nmax,c[20000000],i,nr,j,m;
int main()
{
   freopen("ciur.in","r",stdin);
   freopen("ciur.out","w",stdout);
   scanf("%d",&nmax);
   c[0]=c[1]=1;
   for(i=2;i*i<=nmax;i++)
        if(c[i]==0)
             for(m=2;m*i<=nmax;m++)
                 c[m*i]=1;
    for(i=1;i<=nmax;i++)
        if(c[i]==0)
           nr++;
    printf("%d\n",nr);
    return 0;
}