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

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

else:
    print(1)