#include<bits/stdc++.h>
using namespace std;
const int N = 1000005;
int prime[N], cnt;
bool vis[N];
void get_prime(int n)
{
for (int i = 2; i <= n; i++)
{
if (!vis[i])
prime[cnt++] = i;
for (int j = 0; prime[j] <= n / i; j++)
{
vis[prime[j] * i] = true;
if (i % prime[j] == 0)//prime[j]一定是i的最小质因子，保证了每个合数只会被它的最小质因子筛掉
break;
}
}
}
int main()
{
int n;
cin >> n;
get_prime(n);
cout << cnt;
return 0;
}
