#include <stdio.h>
char v[2000001];
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    int i,j,n,co=0;
    fscanf(fin,"%d",&n);
    for(i=2;i*i<=n;i++)
        if(!v[i])
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
    for(i=2;i<=n;i++)
        if(!v[i])
            co++;
    fprintf(fout,"%d",co);
    fclose(fin);
    fclose(fout);
    return 0;
}