#include <cmath>
#include <iostream>
#include <set>
#include <stdexcept>
#include <string>
int main(){
    int n;
    std::cin>>n;
    std::set<int> s;
    std::cout<<n<<"\n";
    for(int i=1;i<=n;i++){
        int tmp;
        std::cin>>tmp;
        if(s.find(tmp)==s.end()){
            throw std::runtime_error(std::to_string(tmp));
        }
        s.insert(tmp);
    }
}