#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000001> a;

int main()
{
    int i,j,n,c=0;
    fin>>n;
    a[0]=a[1]=1;
    for(i=4;i<=n;i=i+2)
        a[i]=1;
    for(i=3;i*i<=n;i=i+2)
        if(a[i]==0)
        for(j=i*i;j<=n;j+=(2*i))
            a[j]=1;
    c=0;
    for(i=2;i<=n;i++)
    if(a[i]==0) c++;
    fout<<c<<"\n";
    fout.close();

    return 0;
}