#include<stdio.h>
using namespace std;
FILE *f1=fopen("ciur.in","r");
FILE *f2=fopen("ciur.out","w");
int N,i,nr,j;
bool v[2000005];
int main(){
    fscanf(f1,"%d",&N);
    fclose(f1);
     for (i=4;i<=N;i+=2)
        v[i]=1;
    nr=1;
    for (i=3;i<=N;i+=2)
      if (v[i]==0){
            nr++;
            for (j=i+i;j<=N;j+=i)
                v[j]=1;
      }
    fprintf(f2,"%d",nr);
    fclose(f2);
    return 0;
}