#include<fstream>
using namespace std;

bool v[2000002];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n,i,j,m,r=0;
    in>>n;
    v[0]=1;
    v[1]=1;
    for(i=2; i*i<=n; i++){
        if(v[i]==0){
            for(j=2*i; j<=n; j+=i){
                v[j]=1;
            }
        }
    }
    for(i=1;i<=n;i++){
        if(v[i]==0)r++;
    }
    out<<r;
    in.close();
    out.close();
    return 0;
}