n,k = map(int,input().strip().split())
tabs =list(map(int,input().strip().split()))
z=0
ones=0
for i in tabs:
if i == 1:
ones+=1
else:
z+=1
ans=0
visited=[0]*n
for i in range(len(tabs)):
if visited[i] == 1:
continue
zz=z
oo = ones
for j in range(i,len(tabs),k):
visited[j]=1
if tabs[j] == 1:
oo-=1
else:
zz-=1
ans = max(ans,abs(zz-oo))
print(ans)#include <bits/stdc++.h>
using namespace std;
#define int long long int
void testcase()
{
int n , k , allpos = 0 , allneg = 0 , plusclos = 0 , negclos = 0 , answer = 0; cin >> n >> k;
vector<int> v(n);
for(auto &i : v)
{
cin >> i;
i == 1 ? allpos++ : allneg++;
}
for(int b = 0 ; b < n ; b++)
{
for(int i = 0 ; i < n ; i++)
{
if((i - b) % k == 0)
{
v[i] == 1 ? plusclos++ : negclos++;
}
}
plusclos = allpos - plusclos;
negclos = allneg - negclos;
answer = max(answer , abs(plusclos - negclos));
plusclos = 0 , negclos = 0;
}
cout << answer << endl;
}
int32_t main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
clock_t z = clock();
int tc = 1;
// cin >> tc;
while (tc--) testcase();
cerr << "Run Time : " << ((double)(clock() - z) / CLOCKS_PER_SEC) << endl;
return 0;
}
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