#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<map>
#include<queue>
#include<cmath>
#include<stack>
#include<vector>
#include<cstdio>
#define MAXN 2555
#define INF 0x3f3f3f3f
#define v first
#define b second
using namespace std;
const int N = 1000000;
bool prime[N];
int p[N],tot=0;
void init(){
    for(int i = 2; i < N; i ++) prime[i] = true;
    for(int i = 2; i < N; i++){
        if(prime[i]) p[tot ++] = i;
        for(int j = 0; j < tot && i * p[j] < N; j++){
            prime[i * p[j]] = false;
            if(i % p[j] == 0) break;
        }
    }
}

int main()
{
   init();
   int n;
   while(scanf("%d",&n)==1)
   {
      int sum=0;
      for(int i=0;i<tot;i++)
      {
         if(p[i]<=n)
            sum++;
         else break;
      }
      cout<<sum<<endl;
   }
   return 0;
}