n = int(input())
A = [0]*n
B = [0]*n
for i in range(n-1):
    A[i+1],B[i+1] = map(int,input().split())

AS = sum(A)
BS = sum(B)

ans = 0
for a in range((n+2)*10**4):
    b = a+AS-BS
    if b < 0:
        continue
    A[0],B[0] = a,b
    sa = AS+a
    sb = BS+b
    ok = 1
    for na,nb in zip(A,B):
        if na > sb-nb or nb > sa-na:
            ok = 0
    ans += ok

print(ans)