题解

因打字过快有错请纠正，打在评论区，多多点赞哦！

#include<bits/stdc++.h>
using namespace std;
int main() {
	string s;
    int st;
    cin >> s >> st;
    string a = "";
    for (int i = 0; i < s.size(); i++) {
        int t = s[i] - 'A' + st;
        string b = "";
        while (t != 0) {
            b += t % 10 + '0';
            t /= 10;
        }
        for (int i = b.size() - 1; i >= 0; i--)
            a += b[i];
    }
    while (a.size() > 2 && a != "100") {
        string t = "";
        for (int i = 0; i < a.size() - 1; i++){
            int n = (a[i] - '0' + a[i+1] - '0') % 10;
            t += char(n + '0');
        }
        a = t;
    }
    while (a[0] == '0') a.erase(0, 1);
    cout << a;
	return 0;
}