#include<stdio.h>
char c[2000005];
int main()
{
	long i,n,j,nr=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%ld",&n);
	for(i=2;i<=n;i++)
	    c[i]=1;
	for(i=2;i*i<=n;i++)
        if(c[i]==1)
			for(j=i*i;j<=n;j+=i) 
				c[j]=0;
    for(i=2;i<=n;i++)
        if(c[i]==1) nr++;
	printf("%ld",nr);
	return 0;
}