Python 3, 114 110 109 bytes

Actually would have taken two bytes less in Python 2 because exec is a statement and doesn't need parentheses...

• Saved 4 extra bytes thanks to @ElPedro

• Saved an extra byte by taking advantage of the fact that find returns -1 on error, which can then be used as an index

i=0;exec(";".join("i+=1 i-=1 i*=2 i/=2 print(i) exit()".split()["idmhP".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...

Python 3, 114 110 109 116 bytes

Actually would have taken two bytes less in Python 2 because exec is a statement and doesn't need parentheses...

• Saved 4 extra bytes thanks to @ElPedro

• Saved an extra byte by taking advantage of the fact that find returns -1 on error, which can then be used as an index

• +7 bytes because I hadn't noticed the no-newlines rule :(

i=0;exec(";".join("i+=1 i-=1 i*=2 i/=2 print(i,end='') exit()".split()["idmhP".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...

Python 3, 114 110 bytes

Saved 4 extra bytes thanks to @ElPedro

i=0;exec(";".join("i+=1 i-=1 i*=2 i/=2 print(i) exit()".split()["idmhPe".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...

Python 3, 114 110 109 bytes

Actually would have taken two bytes less in Python 2 because exec is a statement and doesn't need parentheses...

• Saved 4 extra bytes thanks to @ElPedro

• Saved an extra byte by taking advantage of the fact that find returns -1 on error, which can then be used as an index

i=0;exec(";".join("i+=1 i-=1 i*=2 i/=2 print(i) exit()".split()["idmhP".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...

Python 3, 114 bytes

i=0;exec(";".join(("i+=1","i-=1","i*=2","i/=2","print(i)","exit()")["idmhPe".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...

Python 3, 114 110 bytes

Saved 4 extra bytes thanks to @ElPedro

i=0;exec(";".join("i+=1 i-=1 i*=2 i/=2 print(i) exit()".split()["idmhPe".find(h[0])]for h in input().split()))

Try it online!

Maps the first character of every input word to a piece of Python code. These are then concatenated and execed.

Pretty straightforward approach, that could probably be golfed a bit more. The difficulty mostly resides in finding the shortest form out of many possible ones...