0pts求助

#include<bits/stdc++.h>
using namespace std;
const int  N = 15; 
int sum;
int main(){
    char a[N + 5];
    for(int i=1;i<=13;i++){
        cin>>a[i];
        if(a[i]!='-' && i!=13){
            sum = sum + i * (a[i] - '0');
        }
    }
    if(sum%11 == (a[13] - '0')&&(sum%11 == 10 && a[13] == 'X')){
        cout<<"Right"<<endl;
    }
    else {
        if(sum%11 == 10){
            a[13] = 'X';
        }
        else a[13] = char(sum%11);
        for(int i=1;i<=13;i++){
            cout<<a[i];
        }
        cout<<endl;
    }
    return 0;
}