#include <iostream>
#include <fstream>
#define MAXN 2000005

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool v[MAXN];

int main()
{
    int i, j, contor, n;
    fin >> n;
    for(i=3; i*i <=n; i+=2)
        if(v[i]==false)
            for(j=i*i; j<=n; j+= 2*i)
                v[j] = true;
    contor = 1;
    for(i=3; i<=n; i += 2)
        if(v[i]==false)
            contor++;
    fout << contor;
    return 0;
}