#include<stdio.h>
char ciur[200000010];
int n,contor,i,j;
void read(), solve();
int main()
{
	read();
	solve();
	return 0;
}
void read()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
}
void solve()
{
	for(i=2;i<=n;++i)
	{
		if(!ciur[i])
		{
			++contor;
			for(j=i+i;j<=n;j+=i)
				ciur[j]=1;
		}
	}
	printf("%d\n",contor);
}