/in/foo.c:1:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main(n){scanf("%d",&n);printf("%d",(n+1)*(n+1)-1);}
 ^~~~
/in/foo.c: In function 'main':
/in/foo.c:1:1: warning: type of 'n' defaults to 'int' [-Wimplicit-int]
/in/foo.c:1:9: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 main(n){scanf("%d",&n);printf("%d",(n+1)*(n+1)-1);}
         ^~~~~
/in/foo.c:1:9: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:1:9: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:1:24: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 main(n){scanf("%d",&n);printf("%d",(n+1)*(n+1)-1);}
                        ^~~~~~
/in/foo.c:1:24: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:1:24: note: include '<stdio.h>' or provide a declaration of 'printf'