n = int(input())
dp0 = [0]
dp1 = [-10**10]
for i in range(n):
    p, a = map(int, input().split())
    dp0.append(max(dp0[i], dp1[i] + p) + p)
    dp1.append(max(dp0[i], dp1[i] + a) + a)
print(max(dp0[-1], dp1[-1]))