Language: C

#define L long long
L n(L a,L b){return a<b?a:b;}
L x(L a,L b){return a>b?a:b;}
#define E(p,q) x(llabs(b*i-p),llabs(b*i-q));
L s(int a,int b){
    L i=0,p=1<<30;
    for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
}
 
int main(void){
    L h,w;
    scanf("%d%d",&h,&w);
	printf("%d",n(s(h,w),s(w,h));
}

Compiler output:
main.c: In function 's':
main.c:4:18: error: implicit declaration of function 'llabs' [-Wimplicit-function-declaration]
    4 | #define E(p,q) x(llabs(b*i-p),llabs(b*i-q));
      |                  ^~~~~
main.c:7:24: note: in expansion of macro 'E'
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                        ^
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'llabs'
  +++ |+#include <stdlib.h>
    1 | #define L long long
main.c:4:18: warning: incompatible implicit declaration of built-in function 'llabs' [-Wbuiltin-declaration-mismatch]
    4 | #define E(p,q) x(llabs(b*i-p),llabs(b*i-q));
      |                  ^~~~~
main.c:7:24: note: in expansion of macro 'E'
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                        ^
main.c:4:18: note: include '<stdlib.h>' or provide a declaration of 'llabs'
    4 | #define E(p,q) x(llabs(b*i-p),llabs(b*i-q));
      |                  ^~~~~
main.c:7:24: note: in expansion of macro 'E'
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                        ^
main.c:4:44: error: expected ')' before ';' token
    4 | #define E(p,q) x(llabs(b*i-p),llabs(b*i-q));
      |                                            ^
main.c:7:24: note: in expansion of macro 'E'
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                        ^
main.c:7:23: note: to match this '('
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                       ^
main.c:7:22: error: too few arguments to function 'n'
    7 |     for(;i++<a;p=n(p,n(E((a-i)/2*b,b*(a-i-(a-i)/2)),E(b/2*(a-i),(a-i)*(b-b/2)))));
      |                      ^
main.c:2:3: note: declared here
    2 | L n(L a,L b){return a<b?a:b;}
      |   ^
main.c: In function 'main':
main.c:12:5: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
   12 |     scanf("%d%d",&h,&w);
      |     ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | #define L long long
main.c:12:5: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
   12 |     scanf("%d%d",&h,&w);
      |     ^~~~~
main.c:12:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:13:9: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   13 |         printf("%d",n(s(h,w),s(w,h));
      |         ^~~~~~
main.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:13:9: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:13:37: error: expected ')' before ';' token
   13 |         printf("%d",n(s(h,w),s(w,h));
      |               ~                     ^
      |                                     )
main.c:13:38: error: expected ';' before '}' token
   13 |         printf("%d",n(s(h,w),s(w,h));
      |                                      ^
      |                                      ;
   14 | }
      | ~