#include <stdio.h>
#include <math.h>
int main()
{
    int n,i,k,rad,prime; FILE *fin=fopen("ciur.in","r"),*fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    bool v[n]; rad=sqrt(n); prime=0;
    for(k=0;k<n;k++)
        v[k]=1;
    v[0]=v[1]=0;
    for(k=2;k<=rad;k++)
    {
        if(v[k]==1)
            for(i=k;i+k<n;i+=k)
                v[i]=0;
    }
    for(k=2;k<n;k++)
        if(v[k]==1)
            prime++;
    fprintf(fout,"%d\n",prime);
    fclose(fin); fclose(fout);
    return 0;
}