백준 1935번 후위표기식2

n = int(input());
s = list(input());
num = dict();
ret = [];
for i in range(1, 27):
  num[chr(i+64)] = 0;
for i in range(n):
  num[chr(i+65)] = int(input());
for i in s:
  mks = ['+','-','*','/']
  if i not in mks:
    ret.append(num[i]);
  else:
    a = ret.pop();
    b = ret.pop();
    t = str(b)+i+str(a);
    ret.append(eval(t));
print(f'{ret.pop():.2f}');