Converting expression to only use NAND gates
If your expression was: \$f = ¬A ⋅ ¬B ⋅ C ⋅ D + A ⋅ B ⋅ ¬C\$

$$¬A ⋅ ¬B ⋅ C ⋅ D + A ⋅ B ⋅ ¬C$$
deMorgans: Invert expression, change + to ⋅ and invert terms.

$$\overline {\overline {¬A ⋅ ¬B ⋅ C ⋅ D} ⋅ \overline {A ⋅ B ⋅ ¬C}}$$

All NANDs.