how to put marker on plot which is not in continuous

i have already used this code for putting marker in plot, I got graph like this I need to put marker after some cycle, is this can do manualy in graph or what should i change in code, please help me

%this is my program clc X=0:0.002:10;

%ph=90;

A=3.5;

w=2*pi*0.25;

w2=2*pi*0.3;

w3=2*pi*0.35;

Y=A*sin(w*X);

Y1=A*sin(w2*X);

Y2=A*sin(w3*X);

plot(X,Y,X,Y1,X,Y2)

hold on

Xi = X(X>=4.08 & X<=4.36) ;

y2 = Y2(X>=4.08 & X<=4.36) ;

plot(Xi(1:10:end),y2(1:10:end),'sk')

hold on

ill get plot i have attached,

but i need put marker like this image, repeating markers after some cycle, but i have only x values.

how can i do this.

thank you