Find Molecular Mass

The program must accept a string S representing a chemical formula as the input. The program must print the molecular mass for the given chemical formula as the output. The given chemical formula contains the following elements (ElementName -> Symbol -> AtomicMass).
Hydrogen -> H -> 1
Helium -> He -> 4
Carbon -> C -> 12
Nitrogen -> N -> 14
Oxygen -> O -> 16
Magnesium -> Mg -> 24
Sulfur -> S -> 32
Calcium -> Ca -> 40
Copper -> Cu -> 63

Boundary Conditions(s):
1 <= Length of S <= 50

Input Format:
The first line contains S.

Output Format:
The first line contains an integer value representing the molecular mass for the given chemical formula.

Example Input/Output 1:
Input:
H2O

Output:
18

Explanation:
H2O -> 2Hydrogen and 1Oxygen
Molecular Mass = (2 * 1) + 16 = 18.

Example Input/Output 2:
Input:
C3H8O3

Output:
92

Explanation:
C3H8O3 -> 3Carbon, 8Hydrogen and 3Oxygen
Molecular Mass = (3 * 12) + (8 * 1) + (3 * 16) = 92.

Example Input/Output 3:
Input:
CuSO4

Output:
159

Example Input/Output 4:
Input:
C12H15

Output:
159

import re
n=input()
compounds={'H':1,'He':4,'C':12,'N':14,'O':16,'Mg':24,'S':32,'Ca':40,'Cu':63 }
p=re.compile(r'([A-Z][a-z]?)(d+)?')
t=0
for e,pv in re.findall(p,n):
    if pv:
        pv=int(pv)
    else:
        pv=1
    t+=compounds[e]*pv

print(t)