#include <iostream>
#include <fstream>
using namespace std;

fstream fin("ciur.in",ios::in);
fstream fout("ciur.out",ios::out);

#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define DIM 2000005
bool prim[DIM];

int main()
{
    int n,nP = 0;
    fin >> n;
    FOR(i,2,n)
        prim[i] = true;
    FOR(i,2,n)
        if(prim[i] == true){
            ++nP;
            for(int j=i+i;j<=n;j+=i)
                prim[j] = false;
        }
    fout << nP;
    fout.close();
    fin.close();
    return 0;
}