# include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
bool v[2000005];
int n,contor=1;
int main()
{
    long long j,i;
    fin>>n;
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
        {
            contor++;
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
        }
    fout<<contor;
return 0;
}