#include <bits/stdc++.h>
using namespace std;

bitset<2000005> viz;
int n;

inline void kratos(int v)
{
    int i;
    for(i=v;i<=n;i+=v) viz[i]=1;
}

int main()
{
    int sol=1,i;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=3;i<=n;i+=2)
        if(!viz[i])
        {
            sol++;
            kratos(i);
        }
    printf("%d\n",sol);
    fclose(stdin);
    fclose(stdout);
    return 0;
}