#include <bits/stdc++.h>
using namespace std;

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

int n;
map<long long, bool>m;

inline void solve()
{
    m[0] = m[1] = 1;
    int ans = 0;
    for(int i=2;i<=n;++i)
    {
        if(!m[i])
        {
            ans++;
            for(int j=2*i;j<=n;j+=i)
            {
                m[j] = 1;
            }
        }
    }
    fout << ans;
}

int main()
{
    fin >> n;
    solve();
}