#include<iostream.h>
#include<stdio.h>
FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
 int main()
{
int a[2000001];
long n;
long nr=0;
fscanf(f,"%ld\n",&n);
long i,j;
for(i=2;i<=n;i++)
a[i]=1;
a[1]=0;
for(i=2;i<=n;i++)
if(a[i])
{
 nr++;
 for(j=i+i;j<=n;j+=i)
  a[j]=0;
}
fprintf(g,"%ld ",nr);
return 0;
}