a[100000],m;c(int*a,int*b){return*a-*b;}x(int*a,int n,int i){int l=0,u=n;for(;u-l>1;a[m=l+u>>1]>>i&1?u=m:(l=m));return i+1?(*a^a[n-1])>>i&1?1<<i|(l=x(a,u,i-1),l<(m=x(a+u,n-u,i-1))?l:m):x(a,n,i-1):0;}main(n){for(n=-2;~scanf("%d",++n+a););qsort(a,n,4,c);m=!printf("%d",x(a,n,29));}