#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define IOS ios_base::sync_with_stdio(0); cin.tie(0)
#define ALL(a) a.begin(),a.end()
#define SZ(a) ((int)a.size())
#define F first
#define S second
#define REP(i,n) for(int i=0;i<((int)n);i++)
#define pb push_back
#define MP(a,b) make_pair(a,b)
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#ifdef leowang
#define debug(...) do{\
	fprintf(stderr,"%s - %d : (%s) = ",__PRETTY_FUNCTION__,__LINE__,#__VA_ARGS__);\
	_DO(__VA_ARGS__);\
}while(0)
template<typename I> void _DO(I&&x){cerr<<x<<endl;}
template<typename I,typename...T> void _DO(I&&x,T&&...tail){cerr<<x<<", ";_DO(tail...);}
#else
#define debug(...)
#endif
template<typename T1,typename T2>
ostream& operator<<(ostream& out,pair<T1,T2> P){
	out<<'('<<P.F<<','<<P.S<<')';
	return out;
}
//}}}
const ll maxn=300005;
const ll maxlg=__lg(maxn)+2;
const ll INF64=8000000000000000000LL;
const int INF=2000000000;
const ll MOD=ll(1e9+7);
const double PI=acos(-1);
//const ll p=880301;
//const ll P=31;
/*
ll mypow(ll a,ll b){
	ll res=1LL;
	while(b){
		if(b&1) res=res*a%MOD;
		else a=a*a%MOD;
		b>>=1;
	}
	return res;
}
*/


ll digitSum(ll n,ll b){
	ll ret=0;
	while(n){
		ret+=n%b;
		n/=b;
	}
	return ret;
}

int main()
{
	//IOS;
	ll n,s;
	cin>>n>>s;

	for(int i=2;i<320000;i++){
		if(digitSum(n,i)==s){
			cout<<i<<'\n';
			return 0;
		}
	}

	ll meow=n-s;

	for(int i=320000;i>=1;i--){
		if(meow%i) continue;
		ll b=meow/i+1;
		if(n%b+n/b%b+n/b/b==s){
			cout<<b<<'\n';
			return 0;
		} 
	}
	cout<<-1;

	return 0;
}
