N = int(input())
AB = [list(map(int, input().split())) for _ in range(N)]
rem = N
day = 0
S = []
N1 = N - N // 3
for i in range(N):
    a,b = AB[i]
    S.append((a + b * (N1 - 1), a, b))
S.sort()
S = S[:N1]
S.sort(key = lambda x:-x[2])

ans = 0
for i in range(N1):
    _,a,b = S[i]
    ans += a + b * i
print(ans)