#include <fstream>
#include <iostream>
#include <vector>
#include <bitset>
#include <string.h>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <deque>

using namespace std;

const char infile[] = "ciur.in";
const char outfile[] = "ciur.out";

ifstream fin(infile);
ofstream fout(outfile);

const int MAXN = 2000005;
const int oo = 0x3f3f3f3f;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

bitset <MAXN> used;

int main() {
    int cnt = 0;
    int N;
    fin >> N;
    int i;
    for(i = 2 ; i * i <= N ; ++ i) {
        if(!used[i]) {
            ++ cnt;
            for(int j = i + i ; j <= N ; j += i)
                used[j] = true;
        }
    }
    while(i <= N) {
        if(!used[i])
            ++ cnt;
        ++ i;
    }
    fout << cnt << '\n';
    fin.close();
    fout.close();
    return 0;
}