Using the fact that the constant of integration is 0

Question

Radioactive decay the rate of disintegration of a radioactive substance can be described by

dn/dt = n₀(-K)e^-Kt

where n0 is the number of radioactive atoms present when time t is 0, and K is a positive constant that depends on the substance involved.

Using the fact that the constant of integration is 0, integrate dn/dt to find the number of atoms n that are still radioactive after time t.