#include <cstdio>
#include <bitset>
using namespace std;
bitset <2000005>a;

int main () {
	int i,j,c=0,n;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i*i<=n;++i){
		if(a[i]==0){
			for(j=i*i;j<=n;j=j+i){
				a[j]=1;
			}
		}
	}
	for(i=2;i<=n;++i){
		if(a[i]==0)++c;
	}
	printf("%d",c);
	return 0;
}