#include <fstream>
#include <bitset>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
	int n,i,j,b,prime;
    bitset <2000050> f;
    fin>>n;
    f[0]=1;
    f[1]=1;
    for (i=2;i*i<=n;++i)
        if (!f[i])
        {
            b=n/i;
            for (j=i;j<=b;++j)
                 f[i*j]=1;
        }
    for (i=2;i<=n;++i)
        if (!f[i]) prime++;
    fout<<prime<<endl;
}