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#include <bits/stdc++.h>
#define M 1000010
#define pb push_back
#define mp make_pair
#define st first
#define nd second
using namespace std;
int t[M],n,x,mx,ans;

int main(){
    scanf("%d",&n);
    for(int i=1; i<=n; i++){
        scanf("%d",&x);
        t[x]++;
        mx=max(mx,x);
    }
    for(int i=0; i<=mx||t[i]; i++){
        t[i+1]+=t[i]>>1;
        ans=i;
    }
    printf("%d",ans);
    return 0;
}