#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[2000001];
int main()
{
    int nr=2000000;
    for (int i=2;i<=nr;++i)
        if (v[i]==0)
        for (int j=2;j<=nr/i;++j)
        v[i*j]=1;
    int n,c=0;
    fin>>n;
    for (int x=2;x<=n;++x)
        if (v[x]==0) c++;
    fout<<c;
}