#include <bits/stdc++.h>
#define oo 100101010
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<2000005> fr;
int erato(int n)
{
    int cnt = 0;
    for(int i = 2; i <= n; i++)
        if(fr[i] == 0)
        {
            cnt++;
            for(int j = 2 * i; j <= n; j += i)
                fr[j] = 1;
        }
    return cnt;
}
int main()
{
    ios_base::sync_with_stdio(0);
    fin.tie(0);
    fout.tie(0);
    int n;
    fin >> n;
    fout << erato(n);
    return 0;
}