P2334为什么好多RE？

#include <iostream>
#include <cmath>
using namespace std;

long long a[10001], minn=1000000, sum=0;

int main(){
    int n;
    cin >>n;
    for(int i = 1; i <= n; i++){
        minn=1000000;
        cin >> a[i];
        if(i==1){
            sum+=a[i];
            continue;
        }
        for(int j = 1; j<i;j++){
            if(abs(a[j]-a[i])<minn)minn=abs(a[j]-a[i]);
        }
        sum+=minn;
    }
    cout << sum;
    return 0;
}