#include <iostream>
#include <fstream>
#define NMAX 2000010
using namespace std;
ifstream fin("date.in");
ofstream fout("date.out");
int n,nr;
bool v[NMAX];
int main()
{
    fin>>n;
    for(int i=2;i<=n;i++){
        for(int j=i*i;j<=n;j=i+j)
            v[j]=true;
    }
    for(int i=2;i<=n;i++)
        if(!v[i])
            nr++;
    fout<<nr;
    return 0;
}