#include <stdio.h>
#include <math.h>
int n,i,d,j,k;
int main()
{
    FILE* si=fopen("ciur.in","r");
    FILE* so=fopen("ciur.out","w");
    fscanf(si,"%i",&n);
    char v[n+5];
    for(i=2; i<=n; i++) v[i]=1;
    for(i=2; i<=n; i++)
    {
        if(v[i]==1)
        {
            for(j=i; j<=n; j+=i)
            {
                v[j]=0;
            }
            k++;
        }
    }
    fprintf(so,"%i",k);
    fclose(si);
    fclose(so);
    return 0;
}