/*  Erica N  */
#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define int long long
#define ull unsigned long long
#define pii pair<int, int>
#define ps second
#define pf first
#define itn int
#define rd read()
int read(){
    int xx = 0, ff = 1;char ch = getchar();
    while (ch < '0' || ch > '9') {if (ch == '-')ff = -1; ch = getchar();}
    while (ch >= '0' && ch <= '9')xx = xx * 10 + (ch - '0'), ch = getchar();
    return xx * ff;
}
// void write(int out) {
// 	if (out < 0)
// 		putchar('-'), out = -out;
// 	if (out > 9)
// 		write(out / 10);
// 	putchar(out % 10 + '0');
// }
#define cdbg(x...) do { cerr << #x << " -> "; err(x); } while (0)
void err() { cerr << endl; }
template<template<typename...> class T, typename t, typename... A>
void err(T<t> a, A... x) { for (auto v: a) cerr << v << ' '; err(x...); }
template<typename T, typename... A>
void err(T a, A... x) { cerr << a << ' '; err(x...); }


const int N = 3e5 + 5;
const int INF = 1e18;
const int M = 1e7;
const int MOD = 1e9 + 7;



inline int get(int a,int p){
    int res=0;
    while(a){
        res+=a%p;
        a/=p;
    }
    return res;
}

bool check(int i,int a,int b){
    if((a-b)%i)return 0;
    int m=(a-b)/i+1;
    if(m<=1)return 0;
    int j=b-i;
    return i*m+j==a;
}

void solve(){
    int a=rd,b=rd;
    int B=ceil(sqrt(a));
    for(int i=2;i<=B;i++){
        // cdbg(a,i,get(a,i));
        if(get(a,i)==b){
            cout<<i<<endl;
            return ;
        }
    }

    for(int i=1;i<=B;i++){
        if(check(i,a,b)){
            cout<<(a-b)/i+1<<endl;
            return ;
        }
        
    }


    cout<<-1<<endl;
}

signed main() {
    // freopen(".in","r",stdin);
    // freopen(".out","w",stdout);

    int T=rd;
    while(T--){
        solve();
    }


}