Let a and b$,$ respectively, be the absolute minimum and maximum values of the function f$($x$1,$ x$2,..,$ Xn$)=$ x$\}+$ x$3+...+$Xh within the regionx$\}+2$x$2+3$x$3+...+$nx $1.$ Let c be the absolute minimum value of f $($X$1,$ X$2,...,$ Xn$)$ on just the boundary of the region.What is a $+$ b $+$ c$?$