Language: C++

#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-fwhole-program")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-fstrict-overflow")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-skip-blocks")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("-funsafe-loop-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#include <cstdio>
#define ll long long
#define abs(a) ((a)>0?(a):(-a))
#define min(a,b) ((a)<(b)?(a):(b))
using namespace std;
ll n,a[110000],tot,ans=922372036854775805;
int main()
{
	scanf("%lld",&n);
	for(register ll i=1; i<=n; ++i) scanf("%lld",&a[i]),tot+=a[i];	 
	for(register ll i=1; i<=n-1; ++i)
		tot-=2*a[i],ans=min(ans,llabs(tot));
	printf("%lld\n",ans);	
	return 0;
}

Compiler output:
a.cc:21:39: warning: bad option '-fwhole-program' to pragma 'optimize' [-Wpragmas]
   21 | #pragma GCC optimize("-fwhole-program")
      |                                       ^
a.cc:28:41: warning: bad option '-fstrict-overflow' to pragma 'optimize' [-Wpragmas]
   28 | #pragma GCC optimize("-fstrict-overflow")
      |                                         ^
a.cc:30:41: warning: bad option '-fcse-skip-blocks' to pragma 'optimize' [-Wpragmas]
   30 | #pragma GCC optimize("-fcse-skip-blocks")
      |                                         ^
a.cc:44:51: warning: bad option '-funsafe-loop-optimizations' to pragma 'optimize' [-Wpragmas]
   44 | #pragma GCC optimize("-funsafe-loop-optimizations")
      |                                                   ^
a.cc:53:10: warning: bad option '-fwhole-program' to attribute 'optimize' [-Wattributes]
   53 | int main()
      |          ^
a.cc:53:10: warning: bad option '-fstrict-overflow' to attribute 'optimize' [-Wattributes]
a.cc:53:10: warning: bad option '-fcse-skip-blocks' to attribute 'optimize' [-Wattributes]
a.cc:53:10: warning: bad option '-funsafe-loop-optimizations' to attribute 'optimize' [-Wattributes]
a.cc: In function 'int main()':
a.cc:56:25: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   56 |         for(register ll i=1; i<=n; ++i) scanf("%lld",&a[i]),tot+=a[i];
      |                         ^
a.cc:57:25: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   57 |         for(register ll i=1; i<=n-1; ++i)
      |                         ^
a.cc:58:41: error: 'llabs' was not declared in this scope; did you mean 'abs'?
   58 |                 tot-=2*a[i],ans=min(ans,llabs(tot));
      |                                         ^~~~~
a.cc:50:24: note: in definition of macro 'min'
   50 | #define min(a,b) ((a)<(b)?(a):(b))
      |                        ^