#include<fstream>
#define maxn 2000002
using namespace std;

long n, i, j; 
long prim[maxn];

long ciur(long n)
{if(n<=1) return 0;
long nr=1;   
for(i=3; i<=n; i+=2)
   if(prim[i]==0)
     {nr++;
      for(j=i+i; j<=n; j+=i)
         prim[j]=1;
     } 
return nr;        
}

int main()
{freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);
scanf("%d", &n);

printf("%d", ciur(n));   
return 0;
}