/in/foo.c:1:16: warning: return type defaults to 'int' [-Wimplicit-int]
 long long a, b;main(){scanf("%lld%lld", &a, &b);printf("%lld\n", a * b - a - b);}
                ^~~~
/in/foo.c: In function 'main':
/in/foo.c:1:23: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 long long a, b;main(){scanf("%lld%lld", &a, &b);printf("%lld\n", a * b - a - b);}
                       ^~~~~
/in/foo.c:1:23: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:1:23: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:1:49: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 long long a, b;main(){scanf("%lld%lld", &a, &b);printf("%lld\n", a * b - a - b);}
                                                 ^~~~~~
/in/foo.c:1:49: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:1:49: note: include '<stdio.h>' or provide a declaration of 'printf'