483-1

class Solution {
public:
    typedef unsigned long long ull;
    string smallestGoodBase(string n) {
        ull N = stoll(n), maxM = log2(N);
        for(int m=maxM; m>=2; m--){
            ull k = ull(pow(N, 1.0/m));
            ull prod = 1, sum = 1;
            for(int j=1; j<=m; j++){
                prod *= k;
                sum += prod;
            }
            if(sum == N)
                return to_string(k);
        }
        return to_string(N-1);
    }
};