View Compilation Error

0_0_26099886_25581.cpp: In function 'int GCD(int, int)':
0_0_26099886_25581.cpp:21:11: error: a function-definition is not allowed here before '{' token
 int main(){
           ^
0_0_26099886_25581.cpp:43:1: error: expected '}' at end of input
 }
 ^