#include<fstream>
using namespace std;
char v[2000001];
int main()
{long long n,i,j,k=0;
ifstream f("ciur.in");
ofstream g("ciur.out");
f>>n;
for(i=2;i<=n;i++)
 if(!v[i])
     {k++;
      for(j=i*i;j<=n;j+=i)
        v[j]=1;
     }
g<<k;
f.close();
g.close();
return 0;}