#include <fstream>

using namespace std;




bool v[2000000];

int main()
{ifstream in("ciur.in");
ofstream out("ciur.out");
   unsigned long long i,k,n;
   in>>n;
   for(i=2;i<=2000000;i++)
    v[i]=0;
for(i=2;i<=2000000;i++)
    {if(v[i]==0) for(k=2*i;k<=2000000;k=k+i)
        v[k]=1;
    }
k=0;
for(i=2;i<=n;i++)
    if(v[i]==0) k++;
out<<k;

    return 0;
}