#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    int n,many = 0;
    in>>n;
    bool *v = new bool[n+1];
    memset(v,false,(n+1)*sizeof(bool));
    for(int i=2;i*i<=n;i++)
    {
        if(!v[i])
        {
            for(int j=i*i;j<=n;j+=i)
                v[j] = true;
        }
    }
    for(int i=2;i<=n;i++)
        many = (!v[i]) ? many+1:many;
    out<<many<<'\n';
    delete[] v;
    return 0;
}