C :

#include<stdio.h>
int main()
{
    int i,j,n,a[1002];
    while(~scanf("%d",&n))
    {
        for(i=0;i<n;i++)
            scanf("%d",&a[i]);
        for(i=0;i<n;i++)
        for(j=0;j<n-i-1;j++)
        if(a[j]>a[j+1]) {int t=a[j];a[j]=a[j+1];a[j+1]=t;}
        for(i=0;i<n;i+=2)
        {
            if(a[i]!=a[i+1])  {printf("%d\n",a[i]);break;}
        }
    }
    return 0;
}

C++ :

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string.h>
using namespace std;

int n, ans, mx, a[510];
int main()
{
    while(scanf("%d", &n) != EOF)
    {
        memset(a, 0, sizeof(a));
        int t;
        for(int i = 1; i <= n; i++)
        {
            scanf("%d", &t);
            a[t]++;
            if(t > mx)
                mx = t;
        }
        for(int i = 1; i <= mx; i++)
            if(a[i] == 1)
                ans = i;
        printf("%d\n", ans);
    }
    return 0;
}