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#include<bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define PB push_back
typedef long long ll;
typedef long double ld;
#define REP(x,y) for(int x=0;x<(y);x++)
#define ROF(x,y) for(int x=(y);x>0;x--)
#define FOR(x,z,y) for(int x=(z);x<(y);x++)
#define INT(x) int x;scanf("%d",&x)
#define LL(x) ll x;scanf("%lld",&x)
#define CZ(x) char x;scanf(" %c",&x)
typedef pair<int,int> pii;
typedef pair<int,pii> piii;

ll suma;
int t[202000];

int main(){
    INT(n);
    while(n--){
        INT(a);
        t[a]++;
    }
    REP(i,201999)t[i+1]+=t[i]/2;
    for(int i=201999;i>=0;i--){
        if(t[i]){
            printf("%d",i);
            return 0;
        }
    }
}