N=int(input())
a=[0]*N
b=[0]*N
for i in range(N):
    a[i],b[i]=map(int,input().split())

def buy(n, history):
    if n == (N+1)*2//3:
        return 0
    cost = []
    for i in range(N):
        if (history & (1 << i)) != 0:
            continue
        cost.append(a[i]+b[i]*n + buy(n+1, history|(1<<i)))
    return min(cost)

print(buy(0, 0))