#include <cstdio>

char a[2000001];

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