#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
using namespace std;
const int N = 10000010;
int primes[N],cnt;
bool st[N];
void get_primes(int n)
{
for(int i = 2;i<=n;i++)
{
if(st[i]) continue;
primes[cnt++] = i;
for (int j = i + i; j <= n; j += i)
st[j] = true;
}
}
int main()
{
int n;
cin >> n;
get_primes(n);
cout << cnt << endl;
return 0;
}