import heapq

def aa(m):
    c=[]
    while m!=uf[m]:
        c.append(m)
        m=uf[m]
    for i in c:
        uf[i]=m
    return m

n=int(input())
ans=0
uf=[i for i in range(n+1)];hq=[]
for i in range(1,n+1):
    a,b=map(int,input().split())
    ans+=a
    heapq.heappush(hq,[a,0,i])
    if i-1:
        heapq.heappush(hq,[b,i,i-1])
while hq:
    q,w,e=heapq.heappop(hq)
    a,b=aa(w),aa(e)
    if a==b:
        continue
    ans+=q;uf[a]=b
print(ans)