#include <fstream>
#define MaxN 2000001
using namespace std;
int main()
{
    int ct=1,i,j,n;
    bool v[MaxN];
    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    for(i=3;i<=n;i++) v[i]=0;
    for(i=3;i<=n;i+=2)
    {
        if(!v[i])
        {
            ct++;
            for(j=i+i;j<=n;j+=i)
            v[j]=1;
        }
    }
    ofstream fout("ciur.out");
    fout<<ct;
    fout.close();
    return 0;
}