hdu 2095 find your present (2)

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#include<stdio.h>
#include<string.h>
int main()
{
	int m,n,a,b,i;
	while(scanf("%d",&n),n)
	{
		scanf("%d",&b);
		for(i=1;i<n;i++)
		{
			scanf("%d",&a);
			b^=a;
		}
		printf("%d\n",b);
	}
	return 0;
}