0分求助

各位神犇,这段代码我的思路应该没有问题,但是跑评测却是0分,神犇帮忙debug下,谢谢!

#include<iostream>
using namespace std;

int main()
{
    string ISBN;
    cin >> ISBN;
    int sum = 0,n = 1;
    for (int i = 0;i < 13;i++)
    {
        if (ISBN[i] == '-')
        {
            continue;
        }
        sum += (ISBN[i] - '0') * n;
        n++;
    }
    sum = sum % 11;
    char sum_char;
    if (sum < 10)
    {
        sum_char = sum + '0';
    }
    else
    {
        sum_char = 'X';
    }
    if (sum_char == ISBN[12])
    {
        cout << "Right" << endl;
    }
    else
    {
        ISBN[12] = sum_char;
        cout << ISBN << endl;
    }
    return 0;
}