#include <cstdio>
#define MAXN 2000000
char ciur[MAXN+1];
int main(){
    FILE*fi,*fout;
    int i,j,n,con;
    fi=fopen("ciur.in" ,"r");
    fout=fopen("ciur.out" ,"w");
    fscanf(fi,"%d" ,&n);
    for(i=2;i*i<=n;i++)
      if(ciur[i]==0)
        for(j=i*i;j<=n;j+=i)
          ciur[j]=1;
    con=0;
    for(i=2;i<=n;i++)
      if(ciur[i]==0)
        con++;
    fprintf(fout,"%d" ,con);
    fclose(fi);
    fclose(fout);
    return 0;
}