func_code_string: #include <bits/stdc++.h>   using namespace std;   char a[1001][1001];   int d[1001][1001];   int n, m, ans;   int main() {     cin >> n >> m;     for (int i = 1; i <= n; i++)       for (int j = 1; j <= m; j++) cin >> a[i][j];     for (int i = n; i > 0; i--)       for (int j = m; j > 0; j--) {         int cur;         d[i][j] = d[i + 1][j] + d[i][j + 1] - d[i + 1][j + 1];         if (a[i][j] ==  W )           cur = 1;         else           cur = -1;         if (cur != d[i][j]) ans++;         d[i][j] = cur;       }     cout << ans;   }   