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#include <cstdlib>
#include <cstdio>
#include <algorithm>

using namespace std;

const int d = 30;
int A[201718+d];

int main()
{
	int n;
    scanf("%d", &n);
    
    int maxA = 0;
    for(int i = 0; i < n; ++i)
    {
        int a;
        scanf("%d", &a);
        ++A[a];
        maxA = max(a, maxA);
    }
	
    for(int i = 0; i <= maxA; ++i)
    {
        if(i == maxA && A[i] > 1)
            ++maxA;
        
        A[i+1] += A[i]/2; 
    }
    
    printf("%d\n", maxA);
    
    return 0;
}