#include<stdio.h>   
#define NMAX 2000000   
  
  
int main()   
{   
freopen("ciur.in","r",stdin);   
freopen("ciur.out","w",stdout);   
long i,n,nrp=0,d,j;   
char c[NMAX+1]={0};   
scanf("%ld",&n);   
for(i=2;i*i<=n;i++)   
    if(c[i]==0)   
    {   
    for(j=i;i*j<=n;j++)   
        c[i*j]=1;   
    }   
for(i=2;i<=n;i++)   
    if(c[i]==0) nrp++;   
printf("%ld",nrp);   
return 0;   
}