#include <bits/stdc++.h>
using namespace std;
#define rd() ({int __x(0);bool __f(0);char __ch(getchar());while(__ch<'0'||__ch>'9')__f^=__ch=='-',__ch=getchar();while(__ch>='0'&&__ch<='9')__x=(__x<<1)+(__x<<3)+(__ch^48),__ch=getchar();__f?-__x:__x; })
typedef long long ll;
int n, m, k;
int main()
{
    n = rd(), m = rd(), k = rd();
    if (m == 1)
    {
        ll ans = 0, a, b;
        for (int i = 1; i <= n; ++i)
        {
            a = rd() - k;
            if (i != 1)
                b = max(a, a + b);
            else
                b = a;
            ans = max(ans, b);
        }
        printf("%lld\n", ans);
    }
    else if (k == 0)
    {
        ll ans = 0, a, b;
        for (int i = 1; i <= n; ++i)
        {
            a = rd();
            if (i != 1)
                b = max(a, a + b);
            else
                b = a;
            ans = max(ans, b);
        }
        printf("%lld\n", ans);
    }
    else
    {
        ll ans = 0;
        ll sum[10] = {
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
            INT_MIN,
        };
        for (int i = 1; i <= n; ++i)
        {
            int x = rd();
            for (int j = 0; j < m; ++j)
                sum[j] += x;
            sum[i % m] = max(sum[i % m], ll(x)) - k;
            ans = max(ans, *max_element(sum, sum + m));
        }
        printf("%lld\n", ans);
    }
    return 0;
}