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class Solution {
public:
    int titleToNumber(string s) {
        int sum = 0;
        int size = s.length();
        for (int i = 0; i < size; i++) {
            sum += (s[i] - 'A' + 1) * (int)pow(26.0, (size - i - 1));
        }
        return sum;
    }
};