include

using namespace std;
int main()
{
int n,i;
cin>>n;
int a[n];
for(i=0;i<n;i++)
cin>>a[i];

int max=a[n-1];

while(i>0)
{
    if(max>=a[i-1])
        max=max+1;
    else 
        max=a[i-1];
    i--;
}
cout<<max<<endl;

}