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#include <bits/stdc++.h> | |
using namespace std; | |
#define int long long // <-----!!!!!!!!!!!!!!!!!!! | |
#define rep(i,n) for (int i=0;i<(n);i++) | |
#define rep2(i,a,b) for (int i=(a);i<(b);i++) | |
#define rrep(i,n) for (int i=(n)-1;i>=0;i--) | |
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--) | |
#define all(a) (a).begin(),(a).end() | |
#define rall(a) (a).rbegin(),(a).rend() | |
#define printV(v) for(auto&& x : v){cout << x << " ";} cout << endl | |
#define printVV(vv) for(auto&& v : vv){for(auto&& x : v){cout << x << " ";}cout << endl;} | |
#define printP(p) cout << p.first << " " << p.second << endl | |
#define printVP(vp) for(auto&& p : vp) printP(p); | |
typedef long long ll; | |
typedef pair<int, int> Pii; | |
typedef tuple<int, int, int> TUPLE; | |
typedef vector<int> vi; | |
typedef vector<vi> vvi; | |
typedef vector<vvi> vvvi; | |
typedef vector<Pii> vp; | |
// const int inf = 1e9; | |
const int inf = 1e12; | |
const int mod = 1e9 + 7; | |
typedef vector<vector<int>> Graph; | |
int f(int b, int n) { | |
if (n < b) return n; | |
return f(b, n / b) + n % b; | |
} | |
signed main() { | |
std::ios::sync_with_stdio(false); | |
std::cin.tie(0); | |
int n, s; | |
cin >> n >> s; | |
if (n == s) { | |
cout << n + 1 << endl; | |
return 0; // <----!!!!!!!!!!!!! | |
} | |
// b <= sqrt(n) は全探索 | |
for (int b = 2; b * b <= n; b++) { | |
if (f(b, n) == s) { | |
cout << b << endl; | |
return 0; | |
} | |
} | |
// b > sqrt(n)のとき | |
// nはb進数で高々2桁なので、 <---!!!!!!!!! | |
// n = pb+q | |
// s = p+q | |
// -> n-s = p(b-1) | |
// ∴ bはn-sの約数+1 | |
int ans = inf; | |
for (int d = 1; d * d <= n - s; d++) { | |
if ((n - s) % d == 0) { | |
int b = d + 1; | |
if (f(b, n) == s) { | |
ans = min(ans, b); | |
} | |
b = (n - s) / d + 1; | |
if (f(b, n) == s) { | |
ans = min(ans, b); | |
} | |
} | |
} | |
cout << (ans == inf ? -1 : ans) << endl; | |
} |
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