#include <bits/stdc++.h>

using namespace std;

#define     mp              make_pair
#define     fs              first
#define     sc              second
#define     pob             pop_back
#define     pub             push_back
#define     eps             1E-7
#define     sz(a)           a.size()
#define     count_one       __builtin_popcount;
#define     count_onell     __builtin_popcountll;
#define     fastIO          ios_base::sync_with_stdio(false)
#define     PI              (acos(-1.0))
#define     linf            (1LL<<62)//>4e18
#define     inf             (0x7f7f7f7f)//>2e9

#ifndef ONLINE_JUDGE
ifstream fin("D:/C++/in");
ofstream fout("D:/C++/out");
#endif

const int MAXN = 2000000/2+1;
bool sieve[MAXN];

void read() {
    int n, nr = 1;

    fin >> n;

    for(int i = 1; (i << 1) + 1 <= n; ++i)
    if(sieve[i] == false) {
        nr++;
        for(int j = i + i + i + 1; (j << 1) + 1 <= n; j += (i << 1) + 1)
            sieve[j] = true;
    }

    fout << nr << "\n";
}

int main() {
	read();

    return 0;
}