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    python solution

    def solve(V): n = len(V) # instead of turning, the ants can be seen to pass each other # so they simply go around and around. # in each direction go about half of them, # meeting the other half 2 times a round, 2x hello in a meeting # 1 round is 10_000 sec, 10**9 sec is 10**5 rounds meets = (n//2) * (n-n//2) * 2 * 2 * 10**5 # now what about the last 6 sec? => must maximize meetings here # 6 sec is 0.6 m per ant, that is ants can only meet if adjacent V.sort() for pos in range(n): if (V[pos]-V[pos-1])%1000 > 1: break run = 0 for i in range(pos, pos+n): if (V[i%n]-V[(i-1)%n])%1000 == 1: run += 1 else: meets += (run+1)//2 * 2 run = 0 else: if run: meets += (run+1)//2 * 2 return meets