foo.c: In function 'main':
foo.c:45:16: warning: format '%lld' expects argument of type 'long long int', but argument 2 has type 'int' [-Wformat=]
     printf("%lld\n",to);
             ~~~^
             %d
foo.c:31:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ^~~~~~~~~~~~~~
foo.c:34:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d",&a[i]);
         ^~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。