ll@n,@m,@t,b[n]{};
rep(m){
	ll@a--;
	b[a]++;
}
ll s=0,r=2d5;
while(s+1<r){
	ll u=s+r>>1;
	ll v=0;
	rep[b](x,n){
		if(x<u){
			v+=(u-x)/t;
		}else{
			v+=(u-x);
		}
	}
	(v<0?s:r)=u;
}
wt(r);