string BigAdd(string s, string t){
    string res;
    int sz = max(s.size(), t.size());
    reverse(s.begin(), s.end());
    reverse(t.begin(), t.end());
    char carry = '0';
    int e = 0, f = 0;
    for(int i = 0; i < sz || carry != '0'; i++){
       e = (i >= s.size() ? 0 : s[i] - '0');
       f = (i >= t.size() ? 0 : t[i] - '0');
       int tmp = (carry - '0') + e + f;
       carry = (tmp/10) + '0';
       res.push_back(tmp%10 + '0');
    }
    reverse(res.begin(), res.end());
    while(res[0] == '0') res.erase(res.begin());
    return res;
}

string BigMulti(string s, string t){
    string res;
    reverse(s.begin(), s.end());
    reverse(t.begin(), t.end());
    for(int i = 0; i < t.size(); i++){
       string tmp = string(i, '0');
       char carry = '0';
       for(int j = 0; j < s.size(); j++){
           int m = (t[i]-'0') * (s[j]-'0') + (carry - '0');
           carry = (m/10) + '0';
           tmp.push_back(m%10 + '0');
       }
       tmp.push_back(carry);
       reverse(tmp.begin(), tmp.end());
       res = BigAdd(res, tmp);
    }
    while(res[0] == '0') res.erase(res.begin());
    return res;
}