from operator import itemgetter


n = int(input())
info = [list(map(int, input().split())) for i in range(n)]
INF = 10 ** 18


info.sort(key=itemgetter(0))
info.sort(key=itemgetter(1), reverse=True)
dp = [[INF] * (n + 1) for i in range(n + 1)]
dp[0][0] = 0

cnt = 0
for i in range(n + 1):
    if i % 2 == 0:
        cnt += 1
    else:
        cnt += 2
    if cnt >= n:
        ind = i
        break

for i in range(n):
    # j番目のitemを選ぶ
    val = dp[i][0]
    for j in range(n):
        a, b = info[j]
        val = min(val, dp[i][j])
        dp[i + 1][j + 1] = min(val + a + b * i, dp[i + 1][j + 1])

print(dp[ind + 1][-1])