880

class Solution {
public:
    string decodeAtIndex(string S, int K) {
       long long len=0;
        vector<char> v;

        for(char c: S){
            if(isdigit(c)) len = len*(c-'0');
            else len += 1;
        }

        for(int i=S.size()-1; i>=0; i--){
            K %= len;
            if(!K && isalpha(S[i]))
                return string(1, S[i]);
            if(isdigit(S[i]))
                len /= (S[i]-'0');
            else
                len--;
        }
        return "";

    }
};