#include<fstream>
using namespace std;
ifstream F("ciur.in");
ofstream G("ciur.out");
int n,i,j;
bool p[2000001];
int main()
{
    F>>n;
    for(i=3;i*i<=n;i+=2)
        if(!p[i])
            for(j=i*i;j<=n;j+=2*i)
                p[j]=1;
    for(j=0,i=3;i<=n;i+=2)
        if(p[i])
            ++j;
    G<<((n+1)/2-j);
    return 0;
}