#include <stdio.h>
#define nmax 2000001
//numere prime mai mici ca nmaxS
char v[nmax];

int main(){
  long int i=2,j,N,nr=0;
  
  FILE *fin=fopen("ciur.in","r");
  fscanf(fin,"%ld",&N);
  //toate nr prime m mici ca N
  FILE *fout=fopen("ciur.out","w");
  while(i<=N){
      if(!v[i]){
        //deci i e numar prim
        //fprintf(fout,"%d ",i);
        nr++;
        //notez in tot vectorul
         for(j=i;j<=N;j+=i)
             v[j]=1;
      }
   i++;
  }
   fprintf(fout,"%ld ",nr);
return 0;
}