#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

void test(){
    int m = 625;
    map<int, int> cnt;
    for(int x = 0; x < m; x++){
        int y = (x*x)%m;
        if(cnt.count(y)) cnt[y]++;
        else cnt[y] = 1;
    }
    for(auto [x, c]: cnt) cout << x << ":" << c << " ";
    cout << endl;
}

const ll N = 1<<29;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    // test();
    ll n, e; cin >> n >> e;
    ll x = 1;
    for(int i = 0; i < e; i++) x *= 5;
    if(e <= 4){
        for(ll r = 0; r < x; r++){
            ll d = abs(n-r*r);
            if(d%x == 0){
                cout << r << endl;
                return 0;
            }
        }
        cout << "NaN" << endl;
        return 0;
    }
    const ll m = 625;
    ll rem = n%m;
    rem = (rem+m)%m;
    vector<int> rr;
    for(int i = 0; i < m; i++){
        if((i*i)%m == rem) rr.push_back(i);
    }
    for(ll i = 0; i*m < x;  i++){
        for(ll a: rr){
            ll r = i*m+a;
            ll d = abs(n-r*r);
            if(d%x == 0){
                if(n <= N){
                    cout << r << endl;
                    return 0;
                }
                while(true){
                    n -= x;
                    if(n >= -N){
                        if(n <= N){
                            cout << r << endl;
                            return 0;
                        }       
                    }else{
                        break;
                    }
                }
            }
        }
    }
    cout << "NaN" << endl;
    return 0;
}