#include <iostream>
#include <fstream>
#define nmax 2000001
using namespace std;

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

bool seen[nmax];
int n, nr;

int main(){
    fin >> n;
    for(int i=4; i<=n; i+=2)    seen[i]= true;
    for(int i=3; i<=n; i+=2)
        if(!seen[i])
            for(int j=i*2; j<=n; j+=i)  seen[j]= true;
    for(int i=2; i<=n; i++)
        if(!seen[i])    nr++;
    fout << nr;
    return 0;
}