rt，机构网站 AC 了。

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;

using LL = long long;

const LL N = 1005;
const LL Inf = 0x7f7f7f7f;

LL a[N][N], f[N][N];

int main()
{
    LL n, m, c;
    cin >> n >> m >> c;
    for (LL i = 1; i <= n; i++)
        for (LL j = 1; j <= m; j++)
            cin >> a[i][j];
    memset(f, Inf, sizeof f);
    LL ans = Inf;
    for (LL i = 1; i <= n; i++)
        for (LL j = 1; j <= m; j++)
        {
            f[i][j] = min(f[i][j - 1], f[i - 1][j]);
            ans = min(ans, a[i][j] + 1LL * c * (i + j) + f[i][j]);
            f[i][j] = min(f[i][j], a[i][j] - 1LL * c * (i + j));
        }
    for (LL i = 1; i <= n; i++)
        reverse(a[i] + 1, a[i] + 1 + m);
    memset(f, Inf, sizeof f);
    for (LL i = 1; i <= n; i++)
        for (LL j = 1; j <= m; j++)
        {
            f[i][j] = min(f[i][j - 1], f[i - 1][j]);
            ans = min(ans, a[i][j] + 1LL * c * (i + j) + f[i][j]);
            f[i][j] = min(f[i][j], a[i][j] - 1LL * c * (i + j));
        }
    cout << ans;
    return 0;
}