#include <stdio.h>

int main(){
    FILE *fin,*fout;
    int n,i,ct,j;
    char v[2000000];

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