27 задача

#f = open('27.txt')
#f = open('27_A.txt')
f = open('27_B.txt')
a = []
fl = 0
for i in f:
    if fl == 0:
        pass
        fl = 1
    else:    
        a.append(i.split())

for i in a:
    i[0] = int(i[0])
    i[1] = int(i[1])
    

#a = [[1,100],[2,200],[5,4],[7,3],[8,2],[10,190]]
#b = 96
b = 36
smax = 0
nsum = 0
for i in a:
    s = i[0]
    if i[1]%b == 0:
        n = i[1]//b
    else:
        n = i[1]//b+1
    p = s*n
    #print(p)
    
    smax = smax + p
    nsum = nsum + n
    
#print(smax)
#print(nsum)


rez = 1000000000000000000
nold_sum = 0
sold = 0
sdelt = 0
sdelt2 = 0
nold=0
for i in a:
    #print('=====')
    s = i[0]
    if i[1]%b == 0:
        n = i[1]//b
    else:
        n = i[1]//b+1        

    p = smax - (nsum-nold_sum) * s    
    
    sdelt = sdelt + nold * sold

    skv = nold_sum * s
    sdelt2 = (skv - sdelt)

    p = p - sdelt + sdelt2
    #print(p)

    if p < rez:
        rez = p

    nold = n
    sold = s
    nold_sum = nold_sum + n

print('ответ = ',rez)