#include <cstdio>
#include <iostream>
#include <bitset>
#define nmax 2000010
using namespace std;

int n,sol;
bitset<nmax> is;

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

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