#include #include #include #include #include #include #include #include using namespace std; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repe(i,x,n) for(int i=x; i<(n); ++i) using ll = long long; using P = pair; #define pai 3.1415926535897932384 #define INF 100100100 #define _GLIBCXX_DEBUG #define All(a) (a).begin(),(a).end() #define rAll(a) (a).rbegin(),(a).rend() int main() { int A,C; char B,D; cin >> A >> B >> C >> D; if(A>C) { cout << "null" << endl; } else if(A