var GET=(function(){function f(s){return new g(s);}function g(s){this._s=s.trim().split("\n");this._y=0;}g.prototype.a=function(f){var s=this._s, y=this._y, r;if(typeof s[y]==="string")s[y]=s[y].split(" ").reverse();r=s[y].pop();if(!s[y].length)this._y++;return f?r:+r;};g.prototype.l=function(f){var s=this._s[this._y++].split(" ");return f?s:s.map(a=>+a);};g.prototype.m=function(n,f){var r=this._s.slice(this._y,this._y+=n).map(a=>a.split(" "));return f?r:r.map(a=>a.map(a=>+a));};g.prototype.r=function(n,f){var r=this._s.slice(this._y,this._y+=n);return f?r:r.map(a=>+a);};return f;})();
var o=GET(require("fs").readFileSync("/dev/stdin","utf8"));

console.log(main());
function main(){
  var n = o.a();
  var a = o.l();
  var l = 1, r = n;
  while(l < r){
    var m = l + r - 2 >> 1;
    var b = Array(a[0]);
    i:
    for(var i = 1; i < n; i++){
      b.length = a[i];
      if(a[i] > a[i-1])continue;
      var f = 1;
      for(var j = b.length - 1; j >= 0; j--){
        if(b[j] === undefined)b[j] = 0;
        if(b[j] >= m)continue;
        b[j]++;
        for(var k = j+1; k < b.length; k++)b[k] = 0;
        f = 0;
        continue i;
      }
      break;
    }
    if(f)l = m + 2; else r = m + 1;
  }
  return l;
}