foo.cc:3:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main(){int m1,n1,m2,n2;scanf("%d%d%d%d",&m1,&n1,&m2,&n2);return printf("%d\n",abs(m1*n1-m2*n2)/abs(n1-n2)),0;}
      ^

自豪的采用jd5进行评测(github.com/masnn/jd5)

{"receive":"2020-02-28T03:28:39.602Z","handle":"2020-02-28T03:28:39.602Z","cache_start":"2020-02-28T03:28:39.602Z","read_cases":"2020-02-28T03:28:39.803Z","judge":"2020-02-28T03:28:39.803Z","done":"2020-02-28T03:28:40.172Z"}