using namespace std;
const int N = 1e6 + 5;
int primes[N];
bool st[N];
int cnt;
void get_primes(int n){
for(int i = 2; i <= n; i){
if(!st[i]) primes[cnt] = i;
for(int j = 0; primes[j] <= n / i; j++){
st[primes[j] * i] = true;
if(i % primes[j] == 0) break;
}
}
}
int main(){
int n; cin >> n;
get_primes(n);
cout << cnt << endl;
}