#include<stdio.h>
int a[100],n,k,nr;
void cit()
{
FILE *f=fopen("grupuri.in","r");
fscanf(f,"%d  %d /n",&k,&n);
for (int i=0;i<n;i++)
fscanf(f,"%d",&a[i]);
fclose(f);
}
void ord()
{
int i,j;
for (i=0;i<n;i++)
   for(j=i;j<n;j++)
      if (a[i]>a[j])
	 {
	 int l=a[i];
	 a[i]=a[j];
	 a[j]=l;
	 }
}
void main()
{
int t;
cit();
while (a[n-k]>0)
    {
    for ( t=n-1;t>n-k;t--)
    a[t]--;
    nr++;
    ord();
    }
nr--;
FILE *f=fopen("grupuri.out","w");
fprintf(f,"%d",nr);
fclose(f);
}