#include <iostream>
#include <bitset>
#define nmax 2000001

using namespace std;
bitset<nmax> pr;
long long i=0,j=0;


int main() {
    int n,nr=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin >> n;
    for(i=2;i<=nmax;++i){
        if(pr[i]==0){
            if(i<=n)
                ++nr;
            for(j=i*i;j<=nmax;j+=i)
                pr[j]=1;
        }
    }
    cout << nr;

    return 0;
}