Language: C++

int main(){
  ll x,k,d;
  cin >> x >> k >> d;
  if(x<0) x*=(-1);
  ll a = abs(x/d);
  ll b = abs(x%d);
  ll c = k-a;
  ll y = abs(d-x);
  if(a>0){
    if(a>=k){

      return cout << abs(x-a*k) << endl,0;
    }
    else {
      if(b<=abs(b-d)){
        if(c%2==0) return cout << b << endl,0;
        else return cout << abs(b-d) << endl,0;
      }
      else {
        if((c+1)%2==0) return cout << abs(b-d) << endl,0;
        else return cout << b << endl,0;
      }
    }
  }
  else{
    if(y<=x){
      if((k-1)%2==0) return cout << y << endl,0;
      else return cout << x << endl,0;
    }
    else {
      if(k==1) return cout << min(y,x) << endl,0;
      c = k-a-1;
      a = abs(y/d);
      b = abs(y%d);
      if(a>=c) return cout << abs(y-d*a) << endl,0;
      else {
        if(b<=abs(b-d)){
          if(c%2==0) return cout << b << endl,0;
          else return cout << abs(b-d) << endl,0;
        }
        else {
          if((c+1)%2==0) return cout << abs(b-d) << endl,0;
          else return cout << b << endl,0;
        }
      }
    }
  }
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:2:3: error: 'll' was not declared in this scope
    2 |   ll x,k,d;
      |   ^~
a.cc:3:3: error: 'cin' was not declared in this scope
    3 |   cin >> x >> k >> d;
      |   ^~~
a.cc:3:10: error: 'x' was not declared in this scope
    3 |   cin >> x >> k >> d;
      |          ^
a.cc:3:15: error: 'k' was not declared in this scope
    3 |   cin >> x >> k >> d;
      |               ^
a.cc:3:20: error: 'd' was not declared in this scope
    3 |   cin >> x >> k >> d;
      |                    ^
a.cc:5:5: error: expected ';' before 'a'
    5 |   ll a = abs(x/d);
      |     ^~
      |     ;
a.cc:6:5: error: expected ';' before 'b'
    6 |   ll b = abs(x%d);
      |     ^~
      |     ;
a.cc:7:5: error: expected ';' before 'c'
    7 |   ll c = k-a;
      |     ^~
      |     ;
a.cc:8:5: error: expected ';' before 'y'
    8 |   ll y = abs(d-x);
      |     ^~
      |     ;
a.cc:9:6: error: 'a' was not declared in this scope
    9 |   if(a>0){
      |      ^
a.cc:12:14: error: 'cout' was not declared in this scope
   12 |       return cout << abs(x-a*k) << endl,0;
      |              ^~~~
a.cc:12:22: error: 'abs' was not declared in this scope
   12 |       return cout << abs(x-a*k) << endl,0;
      |                      ^~~
a.cc:12:36: error: 'endl' was not declared in this scope
   12 |       return cout << abs(x-a*k) << endl,0;
      |                                    ^~~~
a.cc:15:10: error: 'b' was not declared in this scope
   15 |       if(b<=abs(b-d)){
      |          ^
a.cc:15:13: error: 'abs' was not declared in this scope
   15 |       if(b<=abs(b-d)){
      |             ^~~
a.cc:16:12: error: 'c' was not declared in this scope
   16 |         if(c%2==0) return cout << b << endl,0;
      |            ^
a.cc:16:27: error: 'cout' was not declared in this scope
   16 |         if(c%2==0) return cout << b << endl,0;
      |                           ^~~~
a.cc:16:40: error: 'endl' was not declared in this scope
   16 |         if(c%2==0) return cout << b << endl,0;
      |                                        ^~~~
a.cc:17:21: error: 'cout' was not declared in this scope
   17 |         else return cout << abs(b-d) << endl,0;
      |                     ^~~~
a.cc:17:41: error: 'endl' was not declared in this scope
   17 |         else return cout << abs(b-d) << endl,0;
      |                                         ^~~~
a.cc:20:13: error: 'c' was not declared in this scope
   20 |         if((c+1)%2==0) return cout << abs(b-d) << endl,0;
      |             ^
a.cc:20:31: error: 'cout' was not declared in this scope
   20 |         if((c+1)%2==0) return cout << abs(b-d) << endl,0;
      |                               ^~~~
a.cc:20:51: error: 'endl' was not declared in this scope
   20 |         if((c+1)%2==0) return cout << abs(b-d) << endl,0;
      |                                                   ^~~~
a.cc:21:21: error: 'cout' was not declared in this scope
   21 |         else return cout << b << endl,0;
      |                     ^~~~
a.cc:21:34: error: 'endl' was not declared in this scope
   21 |         else return cout << b << endl,0;
      |                                  ^~~~
a.cc:26:8: error: 'y' was not declared in this scope
   26 |     if(y<=x){
      |        ^
a.cc:27:29: error: 'cout' was not declared in this scope
   27 |       if((k-1)%2==0) return cout << y << endl,0;
      |                             ^~~~
a.cc:27:42: error: 'endl' was not declared in this scope
   27 |       if((k-1)%2==0) return cout << y << endl,0;
      |                                          ^~~~
a.cc:28:19: error: 'cout' was not declared in this scope
   28 |       else return cout << x << endl,0;
      |                   ^~~~
a.cc:28:32: error: 'endl' was not declared in this scope
   28 |       else return cout << x << endl,0;
      |                                ^~~~
a.cc:31:23: error: 'cout' was not declared in this scope
   31 |       if(k==1) return cout << min(y,x) << endl,0;
      |                       ^~~~
a.cc:31:31: error: 'min' was not declared in this scope; did you mean 'main'?
   31 |       if(k==1) return cout << min(y,x) << endl,0;
      |                               ^~~
      |                               main
a.cc:31:43: error: 'endl' was not declared in this scope
   31 |       if(k==1) return cout << min(y,x) << endl,0;
      |                                           ^~~~
a.cc:32:7: error: 'c' was not declared in this scope
   32 |       c = k-a-1;
      |       ^
a.cc:33:11: error: 'abs' was not declared in this scope
   33 |       a = abs(y/d);
      |           ^~~
a.cc:34:7: error: 'b' was not declared in this scope
   34 |       b = abs(y%d);
      |       ^
a.cc:35:23: error: 'cout' was not declared in this scope
   35 |       if(a>=c) return cout << abs(y-d*a) << endl,0;
      |                       ^~~~
a.cc:35:45: error: 'endl' was not declared in this scope
   35 |       if(a>=c) return cout << abs(y-d*a) << endl,0;
      |                                             ^~~~
a.cc:38:29: error: 'cout' was not declared in this scope
   38 |           if(c%2==0) return cout << b << endl,0;
      |                             ^~~~
a.cc:38:42: error: 'endl' was not declared in this scope
   38 |           if(c%2==0) return cout << b << endl,0;
      |                                          ^~~~
a.cc:39:23: error: 'cout' was not declared in this scope
   39 |           else return cout << abs(b-d) << endl,0;
      |                       ^~~~
a.cc:39:43: error: 'endl' was not declared in this scope
   39 |           else return cout << abs(b-d) << endl,0;
      |                                           ^~~~
a.cc:42:33: error: 'cout' was not declared in this scope
   42 |           if((c+1)%2==0) return cout << abs(b-d) << endl,0;
      |                                 ^~~~
a.cc:42:53: error: 'endl' was not declared in this scope
   42 |           if((c+1)%2==0) return cout << abs(b-d) << endl,0;
      |                                                     ^~~~
a.cc:43:23: error: 'cout' was not declared in this scope
   43 |           else return cout << b << endl,0;
      |                       ^~~~
a.cc:43:36: error: 'endl' was not declared in this scope
   43 |           else return cout << b << endl,0;
      |                                    ^~~~