ll@n,@k,@a[n];
ll l=-1,r=2d14;
while(l+1<r){
	ll m=l+r>>1;
	ll o=0,t=0;
	rep(i,n){
		ll j=i+1;
		ll d=m-(a[i]+o);
		if(d>0){
			ll e=d/+j;
			t+=e;
			o+=e*j;
		}
	}
	if(t<=k){
		l=m;
	}else{
		r=m;
	}
}
wt(l);