R, 47 bytes

n=scan();cat(rep(if(n%%2)"/"else"\\",n),sep="")

In R, you have to escape backslashes. the argument sep also has to be fully specified since it comes after .... Thus annoyingly few opportunities to save chars :(

R, 47 46 bytes

n=scan();cat(rep(c("\\","/")[n%%2+1],n),sep="")

In R, you have to escape backslashes. the argument sep also has to be fully specified since it comes after .... Thus annoyingly few opportunities to save chars :(

Thanks to bouncyball for golfing away a byte.