import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
AB=[]
at,bt=0,0
for _ in range(n-1):
  a,b=map(int,input().split())
  AB.append((a,b))
  at+=a
  bt+=b

ans=0
for a in range(n*10000+1):
  b=a+at-bt
  if b<0 or a>bt:
    continue
  else:
    chk=True
    for i in range(1,n):
      if AB[i-1][0]>bt+b-AB[i-1][1]:
        chk=False
    if chk:
      ans+=1
print(ans)