#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int Nmax = 2000000 + 5;
bool v[Nmax];
int n, cnt;

int main()
{
    fin >> n;

    for(int i = 2; i * i<= n; ++i)
        if(!v[i])
        {
            for(int j = i + i; j <= n; j += i)
                v[j]  = 1;
        }

    for(int i = 2; i <= n; ++i)if(!v[i])++cnt;

    fout << cnt;
    return 0;
}