The tricky part is we don't know what its EVs or IVs are, or if Gen VI even uses the same base stat system.

We can, however, do min-max.

Assuming Gen VI uses Gen V's HP calculations, we get 77=((0+(2X)+0/4+100)*35/100)+10.

Subtract 10 from both sides to get 67=((2X+100)*35)/100.

Multiply the right to obtain 67=(70X+3500)/100.

Divide by 100 to obtain 67=.7X+35.

Subtract 35 to get 32=.7X.

Multiply the equation by 1/.7, or 1.42857143, to see that the absolute maximum base HP stat is about 45.

The minimum will be with 31 IVs and 252 EVs.

77=((31+(2X)+252/4+100)*35/100)+10

67=((31+2X+63+100)*35/100)

67=(194+2X)*35/100

67=(70X+6790)/100

67=.7X+67.9

67=.7X+67

X=0

For some reason I feel its base HP won't be zero. So.

also I feel I screwed up somewhere

Build a man a fire, keep him warm for a day.

Set a man on fire, keep him warm for the rest of his life.