def main1(n,ab):
  k=0
  cnt=0
  for i in range(n):
      cnt+=1
      if i%2==1:
          cnt+=1
      if cnt>=n:
          k=i+1
          break
  # k個の商品を買う
  ab.sort(key=lambda x:x[1],reverse=True)
  inf=float('inf')
  dp=[inf]*n
  # dp[j]商品iまででj個買うときの最小
  dp[0]=0
  for i in range(n):
    ndp=dp[:]
    a,b=ab[i]
    for j in range(n-1):
      if dp[j]==inf:continue
      ndp[j+1]=min(ndp[j+1],dp[j]+a+b*j)
    dp=ndp
  return dp[k]
    

if __name__=='__main__':
    n=int(input())
    ab=[list(map(int,input().split())) for _ in range(n)]
    ret1=main1(n,ab)
    print(ret1)