#include<fstream>
#include<cmath>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,d,i,sol,nr,j,r;
char v[2000001]
int main(){
    fin>>n;
    for(i=2;i<=n;i++){
        if (v[i] == 0) {
            sol++;
            for (j=i+i;j<=n;j+=i)
                v[j] = 1;
        }
    }
    fout<<sol;
    return 0;
}