tabela = {'H':1, 'S':32, 'O':16, 'C':12, 'Ca':40, 'Na':23, 'P':31}

def massa(tabela, string):
    molecula = string.split()
    massa_m = 0
    i = 0
    while i < len(molecula):
        if i == (len(molecula) - 1) and molecula[i].isalpha():
            for k in tabela:
                if molecula[i] == k:
                    massa_m += tabela[k]
                    break
		elif molecula[i + 1].isdigit():
			for k in tabela:
				if molecula[i] == k:
					massa_m += int(molecula[i + 1]) * tabela[k]
					break
			i += 2
		else :
			for k in tabela:
				if molecula[i] == k:
					massa_m += tabela[k]
					break
			i += 1
	return massa_m

string = 'C O 2'
print massa(tabela, string)