610 B | 610 chars
d = {
"A": (2, 1),
"B": (2, 2),
"C": (2, 3),
"D": (3, 1),
"E": (3, 2),
"F": (3, 3),
"G": (4, 1),
"H": (4, 2),
"I": (4, 3),
"J": (5, 1),
"K": (5, 2),
"L": (5, 3),
"M": (6, 1),
"N": (6, 2),
"O": (6, 3),
"P": (7, 1),
"Q": (7, 2),
"R": (7, 3),
"S": (7, 4),
"T": (8, 1),
"U": (8, 2),
"V": (8, 3),
"W": (9, 1),
"X": (9, 2),
"Y": (9, 3),
"Z": (9, 4),
" ": (1, 1),
}
p, w = map(int, input().split())
prev = -1
ans = 0
for i in input():
num = d[i][0]
cnt = d[i][1]
if prev == num and prev != 1:
ans += w
ans += cnt * p
prev = num
print(ans)