#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i,p=2,*a,n,k=0;
    FILE *f,*g;
    a=(int*)malloc(n*sizeof(int));
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d ",&n);
    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]!=0)
    k++;
    fprintf(g,"%d",k);
    free(a);
    fclose(f);
    fclose(g);
}