View Compilation Error

0_0_36705863_20320.cpp: In member function 'void tree::upd(int, int, int, int, int)':
0_0_36705863_20320.cpp:103:36: error: 'gcd' was not declared in this scope
   t[v] = gcd(t[v * 2], t[v * 2 + 1]);
                                    ^
0_0_36705863_20320.cpp: In member function 'int tree::get(int, int, int, int, int)':
0_0_36705863_20320.cpp:112:72: error: 'gcd' was not declared in this scope
   return gcd(get(l, r, v * 2, tl, tm), get(l, r, v * 2 + 1, tm + 1, tr));
                                                                        ^
0_0_36705863_20320.cpp: In function 'void solve()':
0_0_36705863_20320.cpp:194:31: error: 'gcd' was not declared in this scope
     int g = gcd(L[j].F, R[k].F);
                               ^
0_0_36705863_20320.cpp:206:31: error: 'gcd' was not declared in this scope
     int g = gcd(L[j].F, R[k].F);
                               ^