/in/foo.c: In function 'main':
/in/foo.c:6:11: warning: format '%ld' expects argument of type 'long int *', but argument 2 has type 'int *' [-Wformat=]
  scanf("%ld",&n);
           ^
/in/foo.c:14:9: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
    num+=abs(s[i]-s[k]);
         ^~~