#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
//#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
//#include<list>
#include<queue>
#include<deque>
#include<algorithm>
//#include<numeric>
#include<utility>
//#include<memory>
#include<functional>
#include<cassert>
#include<set>
#include<stack>
#include<random>

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, -1, 0, 1};
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int A;
    cin >> A;
    for (int x = 2; x <= 100; x++) {
        string ans;
        int a = A;
        while (a) {
            int tmp = a%x;
            if (tmp >= 10) {
                ans = "?";
                break;
            }
            else ans = (char)(tmp+'0') + ans;
            a /= x;
        }
        if (ans == "17") {
            cout << x << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return 0;
}