#include <stdio.h>

int main() {
    int N;
    scanf("%d", &N);

    int A[N];
    for (int i = 0; i < N; i++) {
        scanf("%d", &A[i]);
    }

    int single = 0;
    for (int i = 0; i < N; i++) {
        int count = 0;
        for (int j = 0; j < N; j++) {
            if (A[i] == A[j]) {
                count++;
            }
        }
        if (count == 1) {
            single = A[i];
            break;
        }
    }

    printf("%d\n", single);

    return 0;
}