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