#include<bits/stdc++.h>
using namespace std;
using ll = long long;
//using LL = __int128
#define pi pair<ll, ll>
#define N 1111111
ll k, m, a[N], dp[N][11], f[N], n, ans;
int main(){
	scanf("%lld%lld%lld", &n, &m, &k);
	for(int i = 1 ; i <= n ; i++){
		scanf("%lld", a + i);
	}
	if(n <= 2000){
		for(int i = 1 ; i <= n ; i++)
			a[i] += a[i - 1];
		for(int i = 1 ; i <= n ; i++)
			for(int j = i + 1 ; j <= n ; j++)
				ans = max(ans, a[j] - a[i - 1] - (j - i + 1 + m - 1) / m * k);
		printf("%lld", ans);
		return 0;
	}
	if(k == 0){
		for(int i = 1 ; i <= n ; i++){
			f[i] = max(f[i - 1] + a[i], a[i]);
			ans = max(ans, f[i]);
		}
		printf("%lld", ans);
		return 0;
	}
	if(m == 1){
		for(int i = 1 ; i <= n ; i++)
			a[i] -= k;
		for(int i = 1 ; i <= n ; i++){
			f[i] = max(f[i - 1] + a[i], a[i]);
			ans = max(ans, f[i]);
		}
		printf("%lld", ans);
		return 0;
	}
	dp[0][0] = 0;
	for(int i = 1 ; i <= m ; i++)
		dp[0][i] = -0x3f3f3f3f3f3f3f3f;
	for(int i = 1 ; i <= n ; i++){
		dp[i][0] = max(0ll, dp[i - 1][m - 1] + a[i]);
		for(int j = 2 ; j < m ; j++)
			dp[i][j] = dp[i - 1][j - 1] + a[i];
		dp[i][1] = max(dp[i - 1][0], 0ll) + a[i] - k;
		for(int j = 0 ; j < m ; j++){
			ans = max(ans, dp[i][j]);
		}
	}
	printf("%lld", ans);
	return 0;
}