#include<fstream.h>
char p[2000001],
int N,i=2,n,j;
int main()
{ifstream f("ciur.in");
ofstream g("ciur.out");
f>>N;
for(i=2;i<=N;++i)
 if(!p[i])
 {for(j=2*i;j<=N;j+=i)
   p[j]=1;
  ++n;
 }
g<<n;
return 0;
}