#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <class T>
inline T gcd(T a, T b) {
  while (b) {
    a %= b;
    swap(a, b);
  }
  return a;
}
template <class T>
inline T lcm(T a, T b) {
  return a * b / gcd(a, b);
}
const long long MAXN = 2e6 + 7, K = 200043, M = 2500, INF = 1e18 + 7, LOG = 20;
const long double PI = acos(-1.0);
long long MOD = 1e9 + 7;
template <class T>
T sqr(T a) {
  return a * a;
}
long long mul(long long a, long long b) {
  return ((a % MOD) * (b % MOD)) % MOD;
}
long long sum(long long a, long long b) {
  return ((a % MOD) + (b % MOD)) % MOD;
}
long long sub(long long a, long long b) { return sum(a, MOD - b); }
long long bin_pow(long long a, long long n) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = mul(res, a);
    a = mul(a, a);
    n >>= 1;
  }
  return res;
}
long long inv(long long x) { return bin_pow(x, MOD - 2) % MOD; }
long long sum_digit(long long n, long long b) {
  long long sum = 0;
  while (n > 0) {
    sum += n % b;
    n /= b;
  }
  return sum;
}
void solve() {
  long long n, s;
  cin >> n >> s;
  for (long long b = 2; b * b <= n; ++b) {
    long long sum = sum_digit(n, b);
    if (sum == s) {
      cout << b << '\n';
      ;
      return;
    }
  }
  long long ans = 1e18;
  for (long long c1 = 1; c1 * c1 <= n; ++c1) {
    long long c0 = s - c1;
    long double b = 1.0 * (n - c0) / c1;
    if (b < 2) continue;
    if (abs(b - (long long)b) < 1e-9 && sum_digit(n, (long long)b) == s) {
      ans = min(ans, (long long)b);
    }
  }
  cout << (ans == 1e18 ? -1 : ans) << '\n';
  ;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t-- > 0) solve();
  return 0;
}
