#include<stdio.h>
const long long z=2000000;
int n,prime;
bool c[z];
void ciur()
{
	int j=0;
	for(int i=2;i<=z;++i)
		if(c[i]==false)
			for(j=i+i;i<=z;j+=i)
				c[j]=true;
}
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	ciur();
	for(;n>=1;--n)
	{
		if(c[n]==false)
			++prime;
	}
	printf("%d",prime);
	return 0;
}