// gen nr prime <vmax
#include <iostream>
#include <cstdio>
#include <vector>
#define vmax 2000000
using namespace std;
vector<bool>ciur(vmax,true);

int main()
{
    int i,j,n,nr=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i*i<=n;i++)
      if(ciur[i])
        {
            for(j=i;j*i<vmax;j++) ciur[j*i]=false;
        }
    for(int i=2;i<=n;i++)
       if(ciur[i])nr++;
    printf("%d ",nr);
}