#include<cstdio>
#define lim 2000002
long long  p[lim],v[lim],n;
void citire(){
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%lld",&n);
}
long long ciur (){
	long long  k=0;
	for(int i=2;i<=n;i++)
		if(!v[i]){
			k++;
			for(int j=i+i;j<=n;j+=i)
				v[j]=1;
		}
	return k;
}
int main (){
	citire();
	printf("%lld",ciur());
	return 0;
}