Eighteen coins are arranged in a circle. In the beginning, all eighteen coins show tails. The following two moves are allowed:
- Simultaneously flipping over four consecutive coins (so that tails become heads, and heads become tails); for instance the coins in positions 6,7,8,9 may be flipped simultaneously.
- Simultaneously flipping over two pairs of consecutive coins that are separated by exactly one non-flipped coin; for instance the coins in positions 5,6,8,9 may be flipped simultaneously.
Question: Is it possible to reach the situation where all eighteen coins show heads?