#include <cstdio>

char v[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=0;i<n;i++)
		v[i]=1;
	for(i=2;i<n;i++)
		if(v[i]){
			ct++;
			for(j=2;j<n/i;j++)
				v[i*j]=0;
		}	
	printf("%d",ct);
}