a[' _ '],i;c(int*a,int*b){i=*a-*b;}f(s,l,r,m){for(m=l;m<r&&!(a[m]&1<<s);++m);i=s<0?0:m-l&&m-r?1<<s|(i=fmin(f(s-1,l,m),f(s-1,m,r))):f(s-1,l,r);}main(){for(;~scanf("%d",a+i++););qsort(a+1,*a,4,c);printf("%d",f(29,1,*a+1));}