#include<stdio.h>
int n,i,j,sol;
char a[2000010];
void readd(),solve();
int main()
{
	readd();
	solve();
	return 0;
}
void readd()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
}
void solve()
{
	for(i=2;i*i<=n;i++)
		if(a[i]==0)
			for(j=i*i;j<=n;j=j+i)
				a[j]=1;
	for(i=2;i<=n;i++)
		if(a[i]==0)
			sol++;
	printf("%d",sol);
}