The title says it all.
Boys have to count up till 50, and girls have to count down till -50.
You can't count two times in a row.
Let's suppose that 3 girls counted till -3. So if boys have to count, they will have to start from -3. So if 1 boy counts when the count is -3, he can bring the number to -2.
For a better example, click here.
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ps BATMAN HAS TAKEIN OVER AGAHAHAHAHAHHAAHAHAMAHGAHAHAHAHAJNAMAMHhmHMHMMMAHMHMMHMHMHHMH
Really batman? sighs