#include<stdio.h>
#define N 2000000
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int c[N+1],cnt=0,n,i,j;
	scanf("%d",&n);
	//init
	for(i=2;i<=n;++i) c[i]=1;
	for(i=2;i<=n;++i)
	{
		if(c[i]) //daca i e prim
		{
			cnt++;
			for(j=2*i;j<=n;j+=i) c[j]=0; //eliminam multiplii
		}
	}
	printf("%d",cnt);
	fclose(stdin);
	fclose(stdout);
	return 0;
}