left = []
right = []
with open('input01.txt') as file:
    for line in file:
        left.append(line.split()[0])
        right.append(line.split()[1])
left.sort()
right.sort()
out = 0
for i in range(0,len(left)):
    cnt = 0
    for j in range(0,len(right)):
        if right[j] > left[i]:
            out += int(left[i])*cnt
            break
        elif right[j] == left[i]:
            cnt += 1
print(out)