POJ 3253 Fence Repair

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn=20000+10;
int n;
long long a[maxn];
struct cmp1{
bool operator ()(long long &a,long long &b){
return a>b;
}
};
int r;

int main()
{
while(~scanf("%d",&n))
{
priority_queue<long long,vector<long long>,cmp1>q;
for(int i=1; i<=n; i++)
{
scanf("%lld",&a[i]);
q.push(a[i]);
}
r=n-1;
long long cost=0;
while(r--)
{
long long sum=0;
sum=sum+q.top();q.pop();
sum=sum+q.top();q.pop();
q.push(sum);
cost=cost+sum;
}
printf("%lld\n",cost);
}
return 0;
}