n = int(input())
PA = []
for i in range(n):
    p, a = map(int, input().split())
    PA.append((p, a))
PA.reverse()

ans = 0
for i in range(n):
    p, a = PA[i]
    if i == 0:
        ans += p
        x = p
    else:
        if x+a >= p:
            ans += x+a
            x = a
        else:
            ans += p
            x = p
print(ans)