#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) {
  if (a < b) gcd(b, a);
  long long r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
long long modinv(long long a, long long mod) {
  long long b = mod, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= mod;
  if (u < 0) u += mod;
  return u;
}
namespace NTT {
const int MOD = 998244353;
const long long PR = 3;
void trans(vector<long long> &v, bool inv = false) {
  int n = (int)v.size();
  for (int i = 0, j = 1; j < n - 1; j++) {
    for (int k = n >> 1; k > (i ^= k); k >>= 1)
      ;
    if (i > j) swap(v[i], v[j]);
  }
  for (int t = 2; t <= n; t <<= 1) {
    long long bw = modpow(PR, (MOD - 1) / t, MOD);
    if (inv) bw = modinv(bw, MOD);
    for (int i = 0; i < n; i += t) {
      long long w = 1;
      for (int j = 0; j < t / 2; ++j) {
        int j1 = i + j, j2 = i + j + t / 2;
        long long c1 = v[j1], c2 = v[j2] * w % MOD;
        v[j1] = c1 + c2;
        v[j2] = c1 - c2 + MOD;
        while (v[j1] >= MOD) v[j1] -= MOD;
        while (v[j2] >= MOD) v[j2] -= MOD;
        w = w * bw % MOD;
      }
    }
  }
  if (inv) {
    long long inv_n = modinv(n, MOD);
    for (int i = 0; i < n; ++i) v[i] = v[i] * inv_n % MOD;
  }
}
vector<long long> mult(vector<long long> A, vector<long long> B) {
  int size_a = 1;
  while (size_a < A.size()) size_a <<= 1;
  int size_b = 1;
  while (size_b < B.size()) size_b <<= 1;
  int size_fft = max(size_a, size_b) << 1;
  vector<long long> cA(size_fft, 0), cB(size_fft, 0), cC(size_fft, 0);
  for (int i = 0; i < A.size(); ++i) cA[i] = A[i];
  for (int i = 0; i < B.size(); ++i) cB[i] = B[i];
  trans(cA);
  trans(cB);
  for (int i = 0; i < size_fft; ++i) cC[i] = cA[i] * cB[i] % MOD;
  trans(cC, true);
  vector<long long> res((int)A.size() + (int)B.size() - 1);
  for (int i = 0; i < res.size(); ++i) res[i] = cC[i];
  return res;
}
};  // namespace NTT
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  long long n, s;
  cin >> n >> s;
  if (s > n) {
    cout << -1;
    return 0;
  }
  if (s == n) {
    cout << n + 1;
    return 0;
  }
  for (long long i = 2; i * i <= n; i++) {
    long long tmp = 0;
    long long now = n;
    while (now >= i) {
      tmp += now % i;
      now /= i;
    }
    tmp += now;
    if (tmp == s) {
      cout << i;
      return 0;
    }
  }
  long long k = LLONG_MAX;
  for (long long i = 1; i * i <= n; i++) {
    long long tmp = s - i;
    long long ans = n - tmp;
    if (tmp < 0 || ans <= 0) continue;
    if (ans % i == 0) {
      long long wari = ans / i;
      if (wari > i && wari > tmp) {
        k = min(k, wari);
      }
    }
  }
  if (k == LLONG_MAX) {
    cout << -1;
  } else
    cout << k;
}
