How to implement 4 input nand gate using 2 input nand gate

Question

For me 

one 4-input nand gate could be implemented by five 2-input nand gates is this correct or can we implement using less number of gates

Comments

5, 2-input NAND gates are required

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yes this is what i got

Answer 1

yeah if course its a nice logic buddy

see for one 3 i/p nand gate wants 3 2i/p nand gates----->3*1+0

see for one 4 i/p nand gate wants 5 2i/p nand gates----->4*1+1

see for one 5 i/p nand gate wants 7 2i/p nand gates----->5*1+2

see for one 6 i/p nand gate wants 3 2i/p nand gates----->6*1+3

see for one 7 i/p nand gate wants 11 2i/p nand gates----->7*1+4