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#include <bits/stdc++.h>
#define f first
#define s second
#define MP make_pair
#define PB push_back
#define LL long long
#define pii pair<int,int>
#define pll pair<LL,LL>
#define ALL(V) V.begin(),V.end()
#define f1(a,b) for(int a=1;a<=b;a++)
#define f0(a,b) for(int a=0;a<b;a++)
#define boost ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define endl "\n"
using namespace std;
const int N=1e6+69;
int n,a,t[N],w;
int32_t main(void) {
    scanf("%d", &n);
    f0(i,n) {
        scanf("%d", &a);
        t[a]++;
    }
    f0(i,N-3) {
        if(t[i]!=0) w=i;
        t[i+1]+=(t[i]/2);
    }
    printf("%d\n", w);
}