#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset <2000005> b;
int n;

int Ciur(int n)
{
    int i,j,ct=1;
    b[0]=b[1]=1;
    for(i=4;i<=n;i+=2) b[i]=1;
    for(i=3;i*i<=n;i+=2)
        if(b[i]==0)
            for(j=i*i;j<=n;j+=2*i) b[j]=1;
    for(i=3;i<=n;i+=2) if(b[i]==0) ct++;
    return ct;
}

int main()
{
    fin>>n;
    fout<<Ciur(n)<<'\n';
    fout.close();
    return 0;
}