#include <stdio.h>
#include <stdlib.h>
int ciur(int n)
{
    FILE *g;
    g=fopen("ciur.out","w");
    int i,*a,p=2,k=0;
    a=(int*)malloc(n*sizeof(int));
    for(i=2;i<=n;i++)
    a[i]=1;
    while(p*p<n)
    {
        for(i=2;i<=n/2;i++)
        {a[i*p]=0;}
        p++;
        while(a[p]!=1)
        p++;
        }
    for(i=2;i<=n;i++)
    if(a[i]==1)
    k++;
   return k;
    }
int main()
{
    int n;
    FILE *f,*g;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    fprintf(g,"%d",ciur(n));
    fclose(g);
    fclose(f);
    return 0;
}