#include <stdio.h>

int main()
{
    FILE *fin, *fout;
    int n,j,ok=0,i;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    int v[n+1];
    for(i=0;i<=n;i++)
        v[i]=1;
    v[0]=0;
    v[1]=0;
    for(i=2;i<=n;i++)
    {
        if(v[i]!=0)
            for(j=2*i;j<=n;j=j+i)
                if(j%i==0)
                    v[j]=0;
    }
    for(i=2;i<=n;i++)
        if(v[i]==1)
            ok++;
    fprintf(fout,"%d\n",ok);
    fclose(fin);
    fclose(fout);
    return 0;
}