#include <stdio.h>
#define MAX 2000000

int a[MAX];

int main()
{
	int c=0,i,j;
	FILE *in=fopen("ciur.in","r"),*out=fopen("ciur.out","w");
	int n;
	fscanf(in,"%i",&n);
	for(i=2;i<=n;i++)
	{
		if(a[i]==0)
		{
			c++;
			j=i;
			while(j<n)
			{
				j=j+i;
				a[j]=1;
			}
		}
	}
	fprintf(out,"%i",c);
	
}