def main():
    n=int(input())
    tota=totb=M=0
    for _ in range(n-1):
        a,b=map(int,input().split())
        tota+=a 
        totb+=b 
        M=max(M,a+b)

    ans=0
    for i in range(totb+1):
        j=i+tota-totb 
        if j<0 or j<M-totb:
            continue
        ans+=1
    print(ans)

if __name__ == '__main__':
    main()