#include<bits/stdc++.h>
#define sd(x) scanf("%d",&x)
#define ss(x) scanf("%s",x)
#define sc(x) scanf("%c",&x)
#define sf(x) scanf("%f",&x)
#define slf(x) scanf("%lf",&x)
#define slld(x) scanf("%lld",&x)
#define me(x,b) memset(x,b,sizeof(x))
#define pd(d) printf("%d\n",d);
#define plld(d) printf("%lld\n",d);
#define eps 1.0E-8
// #define Reast1nPeace

typedef long long ll;

using namespace std;

const int INF = 0x3f3f3f3f;

bool p[1000010];

void P(){
	memset(p,1,sizeof(p));
	p[0] = p[1] = 0;
	for(int i = 2 ; i*i<=1000000 ; i++){
		if(p[i]){
			for(int j = i+i ; j<=1000000 ; j+=i){
				p[j] = 0;
			}
		}
	}
}

int main(){
#ifdef Reast1nPeace
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
#endif
	ios::sync_with_stdio(false);
	P();
	
	int n;	
	while(cin>>n){
		int ans = 0;
		for(int i = 1 ; i<=n ; i++){
			if(p[i]){
				ans++;
			}
		}
		cout<<ans<<endl;	
	}
	return 0;
}

