decoupling capacitors for DC-DC converters
The input filter specifications depend on: (1) your source impedance and (2) dynamic frequency of the DC-DC converter (3) the spectrum of your step load. (4) radiated EMI of source current and conducted noise as a result of (1,2,3)

This is a 2-way filter spec.  If you require load regulation noise on the source, the unbalanced load impedance being the input to the DC-DC can generate noise on the source.

Consider the input cap. as a LPF to the source impedance  including path inductance, both DM and CM.  Ideally, you want 0 Ohms and expect a well-designed DC-DC converter from Murata will have dampened chokes with suitable Q's or L/R ratios.  

Design thought experiment


Consider the voltage divider relationship of a repetitive pulse with load impedance and the ESR of your input cap  
define your allowed load ripple voltage error / step load current = Step Zout
Consider the impedance of Cin @ f DC-DC = Zc(f)
be aware that the C*ESR =Tau product is limited by the type and quality of capacitor material &lt; 10us for low ESR e-cap and > 100us for G.P. e-cap. while Ceramic is lower density much much faster Tau.
Now define Z cap in  terms of minimum C and maximum ESR @ f for step load I at output ripple Vpp


To meet all the considerations in the beginning; it may end up being a CM choke with two caps in a CLC or Pi filter with a certain differential attenuation Bode Plot that is trivial to design on Falstad's Analog filter site after you define impedance and  attenuation @f.