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