View Compilation Error

0_0_18104280_2344.cpp:21:1: error: 'mark' does not name a type
 mark[2*maxn] = 1;
 ^
0_0_18104280_2344.cpp: In function 'void solve()':
0_0_18104280_2344.cpp:33:8: error: 'mark' was not declared in this scope
     if(mark[d])
        ^
0_0_18104280_2344.cpp:38:5: error: 'mark' was not declared in this scope
     mark[d] = 1;
     ^