#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
#include <cassert>
using namespace std;

namespace {
  using Integer = long long; //__int128;
  template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
  template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
  template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(int i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
  template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}

  template<class H> void print(const H& head){ cout << head; }
  template<class H, class ... T> void print(const H& head, const T& ... tail){ cout << head << " "; print(tail...); }
  template<class ... T> void println(const T& ... values){ print(values...); cout << endl; }

  template<class H> void eprint(const H& head){ cerr << head; }
  template<class H, class ... T> void eprint(const H& head, const T& ... tail){ cerr << head << " "; eprint(tail...); }
  template<class ... T> void eprintln(const T& ... values){ eprint(values...); cerr << endl; }

  class range{
    long long start_, end_, step_;
   public:
    struct range_iterator{
      long long val, step_;
      range_iterator(long long v, long long step) : val(v), step_(step) {}
      long long operator * (){return val;}
      void operator ++ (){val += step_;}
      bool operator != (range_iterator& x){return step_ > 0 ? val < x.val : val > x.val;}
    };
    range(long long len) : start_(0), end_(len), step_(1) {}
    range(long long start, long long end) : start_(start), end_(end), step_(1) {}
    range(long long start, long long end, long long step) : start_(start), end_(end), step_(step) {}
    range_iterator begin(){ return range_iterator(start_, step_); }
    range_iterator   end(){ return range_iterator(  end_, step_); }
  };

  string operator "" _s (const char* str, size_t size){ return move(string(str)); }
  constexpr Integer my_pow(Integer x, Integer k, Integer z=1){return k==0 ? z : k==1 ? z*x : (k&1) ? my_pow(x*x,k>>1,z*x) : my_pow(x*x,k>>1,z);}
  constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z=1){return k==0 ? z%M : k==1 ? z*x%M : (k&1) ? my_pow_mod(x*x%M,k>>1,M,z*x%M) : my_pow_mod(x*x%M,k>>1,M,z);}
  constexpr unsigned long long operator "" _ten (unsigned long long value){ return my_pow(10,value); }

  inline int k_bit(Integer x, int k){return (x>>k)&1;} //0-indexed

  mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count());

  template<class T> string join(const vector<T>& v, const string& sep){
    stringstream ss; for(int i=0; i<v.size(); i++){ if(i>0) ss << sep; ss << v[i]; } return ss.str();
  }

  string operator * (string s, int k){ string ret; while(k){ if(k&1) ret += s; s += s; k >>= 1; } return ret; }

}

constexpr long long mod = 9_ten + 7;

long long f(long long x, long long b, long long s=0){
  return x<b ? x+s : f(x/b, b, s+x%b);
}

int main(){
  long long n,s;
  cin >> n,s;

  if( s == n ){
    println(n+1);
    return 0;
  }
  if( s>n ){
    println(-1);
    return 0;
  }

  for(long long i=2; i*i<=n; i++){
    if( f(n,i) == s ){
      println(i);
      return 0;
    }
  }

  cerr << "unko" << endl;

  for(long long p=sqrt(n); p>0; p--){
    long long q = s-p;
    long long b = (n-q)/p;
    //if( f(n,b) == s){
    if( b*p + q == n && b>p && b>q && n/b==p && n%b==q){
      println(b);
      return 0;
    }
  }
  println(-1);

  return 0;
}


Measured memory_bytes: 384