#include<bits/stdc++.h>
#define F(i,j,k) for (signed i=signed(j);i<=signed(k);i++)
using namespace std;
int n,m,a[(int)1e4+5],turn,t,now[(int)1e6+5];
main () {
	cin>>n>>m;
	F(i,1,n) cin>>a[i];
	while(turn<n+m){
		F(i,1,m) {
			if(now[i]==0) {
				now[i]=a[++turn];
			}
			now[i]--;
		}
		t++;
	}
	cout<<t-1;
    return 0;
}

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