class Solution:
    def titleToNumber(self, s: str) -> int:
        col_val_dict = {'A':1, 'B':2,'C':3,'D':4,'E':5,'F':6,'G':7,'H':8,'I':9,'J':10,'K':11,'L':12,'M':13,'N':14, 'O':15,'P':16,'Q':17,'R':18,'S':19,'T':20,'U':21,'V':22,'W':23,'X':24,'Y':25,'Z':26}
        last_i = len(s) - 1
        val = 0
        for letter in s:
            val += (26 ** last_i) * col_val_dict.get(letter)       
            last_i -= 1
        
        return val
