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#include <stdio.h>
#define DEF #define
#define RI _ri()
#define RL _rl()
#define RS(x) scanf(" %s",x)
#define WI(x) printf("%d\n",x)
#define WL(x) printf("%lld\n",x)
#define WS(x) puts(x)
#define RAI(x,n) FOR(_i,n) x[_i] = RI
#define RAL(x,n) FOR(_i,n) x[_i] = RL
#define FOR(x,y) for(int x = 0; x < y; x++)
static inline int _ri() { int r, i = scanf(" %d",&r); (void)i; return r; }
static inline int _rl() { long long r, i = scanf(" %lld",&r); (void)i; return r; }
#define N 211718
int t[N];
int main() {
  int n = RI;
  FOR (i, n) t[RI]++;
  int v = 0, max = 0;
  for (int i = 0; i < N; i++) {
    v += t[i];
    if (v) max = i;
    v /= 2;
  }
  WI(max);
  return 0;
}