#include <algorithm> #include <cassert> #include <cmath> #include <cstdio> #include <cstring> #include <iomanip> #include <iostream> #include <map> #include <memory> #include <numeric> #include <set> #include <stack> #include <string> #include <vector> #define rep(i, a, b) for (int i = (a); i < (b); ++i) #define MOD 1000000007 #define int long long using ll = long long; using namespace std; const int INF = 1LL << 50; using P = pair<int, int>; template <class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } else { return false; } } template <class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } else { return false; } } struct Setup { Setup() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); } } SETUP; template <typename T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; } signed main() { int n; cin >> n; if (n == 0) { puts("-1"); return 0; } for (int i = 2; i <= 100; i++) { string s; int k = n; while (k) { s += '0' + k % i; k /= i; } reverse(s.begin(), s.end()); if (s == "17") { cout << i << endl; return 0; } } puts("-1"); }