#include <iostream>


int n;
bool arr[1000001];

int main() {
    freopen("prefmex.in","r",stdin);
    freopen("prefmex.out","w",stdout);

    std::ios::sync_with_stdio(false);
    std::cin.tie(NULL);
    std::cout.tie(NULL);

    std::cin >> n;
    int min = 0;
    for (int i = 0; i < n; ++i) {
        int num;
        std::cin >> num;
        arr[num] = true;

        for (; arr[min]; ++min) {
            ;
        }
        std::cout << min << ' ';
    }
}