#include<fstream>
#include<bitset>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
#define M 2000005
bitset <M> bitsett;

int main(){
    short n,cnt=0;
    cin>>n;
    for(int i=2; i<=n; ++i)
        bitsett[i]=1;
    for(int i=2; i<=n; ++i)
        if(bitsett[i]){
            ++cnt;
            for(int j=i+i; j<=n; j+=i)
                bitsett[j]=0;
        }
    cout<<cnt;
    return 0;
}