import sys

sys.setrecursionlimit(10**6)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def MI(): return map(int, sys.stdin.buffer.readline().split())
def MF(): return map(float, sys.stdin.buffer.readline().split())
def MI1(): return map(int1, sys.stdin.buffer.readline().split())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
inf = 10**16
# md = 998244353
md = 10**9+7

n=II()
ab=LLI(n)
ab.sort(key=lambda x:-x[1])

pay=0
for i in range(1,n+1):
    if i+i//2>=n:
        pay=i
        break

def chmin(i,val):
    if val<dp[i]:dp[i]=val

dp=[inf]*(pay+1)
dp[0]=0
for a,b in ab:
    for i in range(pay-1,-1,-1):
        if dp[i]==inf:continue
        chmin(i+1,dp[i]+a+b*i)

print(dp[-1])