#include <bits/stdc++.h>

using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
bool prim[2000005];
int main()
{
    int i,n,k=0,a,b;
    fin>>n;
    for(i=2;i<=n;++i){
        if(!prim[i]) {
            for(int j=2*i;j<=n;j+=i){
                prim[j]=1;
            }
            k++;
        }

    }
    fout<<k;



    return 0;
}