#include <bits/stdc++.h>
#ifdef Local
#include "debug/debug.h"
#else
#define debug(...)
#endif

typedef long long ll;
typedef long double ld;

#define int ll

#define vec vector
#define str string
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rev(x) reverse(x)
#define sz(x) (int)(x).size()

using namespace std;

void solve() {
    int n, s;
    cin >> n >> s;
    if (n == 1 && s == 1) {
        cout << 2;
        return;
    }
    int b = 2;
    bool r = false;
    for (; b <= (int)1e7; b++) {
        int cur = 0;
        int x = n;
        while (b <= x) {
            cur += x % b;
            x /= b;
        }
        cur += x;
        if (cur == s) {
            r = true;
            break;
        }
    }
    if (!r && n != 1) {
        b = n;
        int cur = 0;
        int x = n;
        while (b <= x) {
            cur += x % b;
            x /= b;
        }
        cur += x;
        if (cur == s)
            r = true;
    }
    if (!r) {
        b = n;
        for (; b >= 2 && b >= n - (int)1e7; b--) {
            int cur = 0;
            int x = n;
            while (b <= x) {
                cur += x % b;
                x /= b;
            }
            cur += x;
            if (cur == s) {
                r = true;
                break;
            }
        }
    }
    cout << (r ? b : -1) << '\n';
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int tt = 1;
    //    cin >> tt;
    while (tt-- > 0)
        solve();

    return 0;
}