#include <bits/stdc++.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int N = 2000010;
bitset<N> p;
int n,cnt;
int main()
{
    //f>>n;
    cin>>n;
    p.flip();
    for(int i=2; i*i<=n; i++)
        if(p[i])
            for(int j=i*i; j<=n; j+=i)
                p[j]=0;
    cnt=p.count()-N+n-1;
    cout<<cnt;
    //g<<cnt;
    return 0;
}