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