formula2.py

def fib(aa, bb, cc):
    if aa <= 0 or bb <= 0 or cc <= 0:
        return 1
    if aa > 20 or bb > 20 or cc > 20:
        return fib(20, 20, 20)
    _dp = [[[1 for _ in range(21)] for _ in range(21)] for _ in range(21)]
    for a in range(1, aa + 1):
        for b in range(1, bb + 1):
            for c in range(1, cc + 1):
                if a < b < c:
                    _dp[a][b][c] = (
                        _dp[a][b][c - 1] + _dp[a][b - 1][c - 1] - _dp[a][b - 1][c]
                    )
                else:
                    _dp[a][b][c] = (
                        _dp[a - 1][b][c]
                        + _dp[a - 1][b - 1][c]
                        + _dp[a - 1][b][c - 1]
                        - _dp[a - 1][b - 1][c - 1]
                    )
    return _dp[aa][bb][cc]


if __name__ == "__main__":
    (a, b, c) = tuple([int(x) for x in input().rstrip().split()])
    print(fib(a, b, c))