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#include <iostream>
using namespace std;

bool tab[201719];
int maximum = 0;

void put(int m){
    if(tab[m] == false){
        tab[m] = true;
        if(m > maximum){
            maximum = m;
        }
    }else{
        tab[m] = false;
        put(m + 1);
    }
}

int main(){
    int n, a;
    cin>>n;
    for(int i = 0; i < n; i++){
        cin>>a;
        put(a);
    }
    cout<<maximum;

return 0;
}