using namespace std;


#include <set>
#include <map>
#include <list>
#include <deque>
#include <stack>
#include <queue>
#include <cmath>
#include <ctime>
#include <cctype>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <utility>
#include <iomanip>
#include <fstream>
#include <cstring>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>

#define oo (1<<30)
#define f first
#define s second
#define II inline
#define db double
#define ll long long
#define pb push_back
#define mp make_pair
#define Size(V) ((ll)(V.size()))
#define all(V) (V).begin() , (V).end()
#define CC(V) memset((V),0,sizeof((V)))
#define CP(A,B) memcpy((A),(B),sizeof((B)))
#define FOR(i,a,b) for(ll (i)=(a);(i)<=(b);++(i))
#define REP(i, N) for (ll (i)=0;(i)<(ll)(N);++(i))
#define FORit(it, x) for (__typeof((x).begin()) it = (x).begin(); it != (x).end(); ++it)
#define printll(x) printf("%lld",(x))
#define printsp() printf(" ")
#define newline() printf("\n")
#define readll(x) scanf("%lld",&(x))
#define debugll(x) fprintf(stderr,"%lld\n",(x))

#define IN "ciur.in"
#define OUT "ciur.out"

//#define ONLINE_JUDGE

const int MAX_COUNT = 2000100;

bool notPrime[MAX_COUNT];

int maxVal;
int primeCount;

int getPrimeCount()
{
  primeCount = 0;
  if (maxVal < 2)
  {
    return primeCount;
  }
  if (maxVal >= 2)
  { 
    primeCount++;
  }
  int num = 3;
  int multiple = 3;
  while (num <= maxVal)
  {
    primeCount++;
    multiple = 2 * num;
    while (multiple <= maxVal)
    {
      notPrime[multiple] = true;
      multiple += num;
    }
    num += 2;
    while (notPrime[num] && num <= maxVal)
    {
      num += 2; 
    }
  }   
  return primeCount;
}

void solve(int test) {
  cin >> maxVal; 
  getPrimeCount();
  cout << primeCount;
}

int main() {
#ifndef ONLINE_JUDGE
  freopen(IN,"r",stdin);
  freopen(OUT,"w",stdout);
#endif
    solve(1);
  return 0;
}