how to find root of equation

k0=(2*pi/0.6328)*1e6;

t2=1.5e-6;

n1=1.512;n2=1.521;n3=4.1-1i*0.211;

n4=1;

m=0;

t3=1e-9;

k1=k0*sqrt(n1^2-x^2);

k2=k0*sqrt(n2^2-x^2);

k3=k0*sqrt(n3^2-x^2);

k4=k0*sqrt(n4^2-x^2);

y=-(k2)*t2+atan(k1/1i*k2)+atan((k3/k2)*tan(atan(k4/1i*k2)-k3*t3))+m*pi;

pl find to help the root of the equation