#include<stdio.h>
#include<string.h>

int n,cnt=0;
char *Prime;//Prime[i]==1 => Prime[i] nu e prim


void pregateste()
{FILE *pin=fopen("ciur.in","r");
fscanf(pin,"%d",&n);
n=44;
Prime=new char[n/16+1];
memset(Prime,0,sizeof(Prime)*(n/16+1));
fclose(pin);}

void rezolva()
{int i,j;
for(i=3;i<=n;i+=2)
  if(( Prime[i/16] & (1<<(i/2%8)))==0)
    {
    cnt++;
    for(j=i*i;j<=n;j+=i*2)
      Prime[j/16]=Prime[j/16]|(1<<(j/2%8));
    }
}

void incheie()
{delete []Prime;
FILE *pout=fopen("ciur.out","w");
fprintf(pout,"%d",cnt+1);
fclose(pout);}

int main()
{
pregateste();
rezolva();
incheie();
return 0;
}