#include <stdio.h>
void swap_elements(int arr[], int n){
    for (int i = 0; i < n - 1; i += 2){
        int temp = arr[i];
        arr[i] = arr[i + 1];
        arr[i + 1] = temp;
    }
}
void print_array(int arr[], int n){
    for (int i = 0, i < n; i++){
        printf("%d", arr[i]);
    }
    printf("\n");
}
int main(){
    int n;
    scanf("%d",&n);
    if (n <= 0){
        printf("-1\n");
        return 0;
    }
int arr[n];
for (int i = 0; i < n; i++);
scanf("%d", &arr[i]);
}
swap_elemens(arr, n);
print_array(arr, n);
return 0;
}