#include <fstream>
 
using namespace std;
 
ifstream in("ciur.in");
ofstream out("ciur.out");
 
bool c[2000001];
 
int main() {
    int n, contor = 0;
    in >> n;
 
    for(int i = 2; i * i <= n; i++)
        if(!c[i])
            for(int j = i * i; j <= n; j += i)
                c[j] = 1;
     
    for(int i = 2; i <= n; i++)
        if(!c[i])
            contor++;
     
    out << contor;
     
    return 0;
}