#include <cstdio>
#include <fstream>
#include <cstdlib>
#include <utility>
#include <algorithm>
#include <bitset>
#include <vector>
#include <map>
#include <queue>
#include <string>
#include <set>
#include <cstring>

#define LL long long
#define F(i, a, b) for (int i = (a) ; i <= (b) ; ++i)
#define V_IN(x) (V).push_back((x))
#define LLU unsigned LL
#define ALL(V) (V).begin(), (V).end()
#define V_sz (V).size()

#define mlb map <LL, bool>
#define MLI map <LL, int>
#define mp make_pair
#define pii pair <int, int>

#define SORT(x) sort ((x).begin(), (x).end() )
#define fi first
#define se second
#define VI vector <int>

using namespace std;

static const int c_max = 2000005;

bitset <c_max> viz;

int p[c_max], prime;

inline void Ciuruialaa(int N, ostream& out){
    for (int i = 3; i <= N; i += 2 )
        viz[i] = 1;
        for (int i = 3; i <= N; i += 2) {
            if (!viz[i])
            continue;
            ++prime;
        for (int j = (i << 1 ) + i; j <= N; j += (i << 1 ) )  viz[j] = 0;
        }
        out << prime + 1;
}

int main(){
    ifstream f ("ciur.in");
    ofstream out ("ciur.out");
    int n;
    f >> n;
    Ciuruialaa(n, out);
    return 0;
}