n = int(input())
admission = 0
out = 0
for _ in range(n-2+1):
    a, b = map(int,input().split())
    admission += a
    out += b

if admission >= out:
    #Aが0のとき
    minimA1 = 0
    minimB1 = admission - out
    
    #Bが最大の時
    maximA1 = out
    maximB1 = admission
    
    print(maximB1-minimB1+1)

else:
    #Aが最小のとき
    minimA1 = out-admission
    
    #Aが最大のとき
    maximA1 = out
    print(maximA1-minimA1+1)