#include <cstdio>

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