#include <stdio.h>

using namespace std;

FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int i,N,k,v[2000000];
unsigned long long j;

int main()
{
    fscanf(f,"%d",&N);
    for(i=3;i<=N;i+=2)
     if(v[i]==0)
      {
          for(j=i*i;j<=N;j+=2*i)
           v[j]=1;
          k++;
      }
    fprintf(g,"%d",k+1);
    return 0;
}