#include<stdio.h>
unsigned long int n,a[20000000],nr;

int main()
{
FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");

fscanf(f,"%d",&n);
int i,j;
for(i=2;i<=n;i++)
a[i]=1;
for(i=2;i<=n/2;i++)
for(j=i;j<=n/i;j++)
a[i*j]=0;
for(i=2;i<=n;i++)
if(a[i])
nr++;
fprintf(g,"%d",nr);
return 0;
}