#include <cstdio>
#include <algorithm>
using namespace std;
FILE *f,*g;
int v[100100];
int n,k,sol,i;
bool ok;

int main() {
f=fopen("grupuri.in","r");
g=fopen("grupuri.out","w");

fscanf(f,"%d%d",&k,&n);

for (i=1;i<=n;i++) 
	fscanf(f,"%d",&v[i]);

ok=true;

sol=0;

while (v[n-k+1]) {
	sol++;
	for (i=n-k+1;i<=n;i++)
		v[i]--;
	sort(v+1,v+n+1);
	}	

fprintf(g,"%d",sol);

fclose(g);
return 0;
}