View Compilation Error

0_0_27034261_11443.cpp:2:11: error: '::main' must return 'int'
 void main()
           ^
0_0_27034261_11443.cpp: In function 'int main()':
0_0_27034261_11443.cpp:5:18: error: 'scanf_s' was not declared in this scope
  scanf_s("%d", &M);
                  ^