#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int ciur[2000002];
int main()
{
    int i,j,n,cnt = 0;
    in >> n;
    for(i=2;i<=n;i++){
        ciur[i] = 1;
    }
    for(i=2;i<n;i++){
        if(ciur[i] == 1){
            cnt++;
            for(j=i+i;j<n;j=j+i){
                ciur[j] = 0;
            }
        }
    }
    out << cnt;
    return 0;
}