#include <stdio.h>

int main(){
    FILE *fin,*fout;
    int n,i,d,ct;

    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    ct=0;
    for(i=2;i<=n;i++){
        d=2;
        if(d*d<i&&i%d!=0){
            i=i+2;
            while(d*d<i&&i%d!=0){
                d++;
            }
        }
        if(d*d>i){
            ct++;
        }
    }
    fprintf(fout,"%d",ct);
    fclose(fin);
    fclose(fout);
    return 0;
}