#include <bits/stdc++.h>
#define nmax 2000000
using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int c[nmax],n;


void ciur()
{int i,j;
 c[2]=1;
 for(i=3;i<=n;i+=2) c[i]=1;

 for(i=3;i*i<=n;i+=2)
    if(c[i]==1)
      for(j=i*3;j<=n;j+=2*i) c[j]=0;
}

int af()
{int i;
 int ct=1;
 for(i=3;i<=n;i+=2)
    if(c[i]==1) ct++;
 return ct;
}

int main()
{int i;
 fscanf(f,"%d",&n);
 ciur();
 int nr=af();
 fprintf(g,"%d",nr);
 return 0;
}