#include <bits/stdc++.h>
using namespace std;


int main() {
    int n;cin>>n;
    int ans = 0;
    for(int i = 0;i<=n;i++){
        long long num = 1ll * i * i;
        string s1 = to_string(i);
        string s2 = to_string(num);
        s2 = s2.substr(s2.size()-s1.size());
        if(s1==s2) ans++;
    }
    cout<<ans;

    return 0;
}