T137288 铸星

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define IL inline
#define RG register
using namespace std;
typedef long long LL;
#define RI RG int
#define RC RG char
const int N=5e5;

    int n;
    LL a[N+3];

int main(){
    scanf("%d",&n);
    for(RI i=1;i<=n;i++)
        scanf("%lld",&a[i]);
        
    if(n==1){
        printf("%lld",a[1]);
        return 0;
        
    }
    
    LL s=0;
    int c=0;
    for(RI i=1;i<=n;i++){
        s+=abs(a[i]);
        c+=(a[i]>0);
        
    }
    
    if(c!=0&&c!=n){
        printf("%lld",s);
        return 0;
        
    }
    
    LL x=-1LL<<60;
    for(RI i=2;i<n;i++)
        x=max(x,abs(a[i]-a[i+1])-abs(a[i])-abs(a[i+1]));
    printf("%lld",s+x);

    return 0;

}