def parse(s: str) -> list[list[int]]:
    return [[int(i) for i in l.split()] 
                for l in s.strip().splitlines()]

def solve(l: list[list[int]]) -> int:
    cache = {}
    n = len(l)
    l = reversed(l)
    for i, row in enumerate(l):
        for j, val in enumerate(row):
            if i == 0:
                cache.update({(i, j): val})
            else:
                l = cache[(i-1, j)]
                r = cache[(i-1, j+1)]
                cache.update({(i, j): val+max(l, r)})
    return cache[(n-1, 0)]

if __name__ == '__main__':
    with open("input", "r") as f:
        input = f.read()
    print(solve(parse(input)))