I have to create a circuit using NOR gates which gives an ouput of 1 if 3 or 4 inputs agree

I created the truth table and got the following

f = (a'b'c'd')+(a'b'c'd)+(a'b'cd')+(a'bc'd')+(a'bcd)+(ab'c'd')+(ab'cd)+(abcd')+(abcd)

I then used a Karnaugh map and got

f = (a'b'c')+(a'b'd')+(b'c'd')+(a'c'd')+(bcd)+(abd)+(abc)+(acd)

I am struggling and cannot seem to find a way to build the circuit.

Can anyone point me in the right direction?

Any help or pointers would be greatly appreciated.