func_code_string: #include <bits/stdc++.h>   using namespace std;   char ans[10][10];   long long dp[10][513][513];   pair<pair<long long, long long>, long long> recur[10][513][513];   long long insert[10][513][513];   long long curr, nexty, n, m;   long long setBit(long long num, long long i) { return num | (1 << i); }   long long unsetBit(long long num, long long i) {     num ^= 1 << i;     return num;   }   bool checkBit(long long num, long long i) {     if (num & 1 << i)       return true;     else       return false;   }   string binary(long long num, long long m) {     string ans;     for (long long i = 0; i < m; i++) {       if (checkBit(num, i))         ans =  1  + ans;       else         ans =  0  + ans;     }     return ans;   }   void backtrack(long long j, long long mask1, long long mask2, long long mask3,                  long long newT, long long ogmask1, long long ogmask2,                  long long ts) {     if (j == m) {       if (dp[curr][ogmask1][ogmask2] + newT > dp[nexty][mask2][mask3]) {         dp[nexty][mask2][mask3] = dp[curr][ogmask1][ogmask2] + newT;         recur[nexty][mask2][mask3] = pair<pair<long long, long long>, long long>(             pair<long long, long long>(ogmask1, ogmask2), mask1);         insert[nexty][mask2][mask3] = ts;       }       return;     }     if (j > 1) {       if (!checkBit(mask1, j) && !checkBit(mask1, j - 1) &&           !checkBit(mask1, j - 2) && !checkBit(mask2, j - 1) &&           !checkBit(mask3, j - 1)) {         long long tempmask1 = setBit(mask1, j);         tempmask1 = setBit(tempmask1, j - 1);         tempmask1 = setBit(tempmask1, j - 2);         backtrack(j + 1, tempmask1, setBit(mask2, j - 1), setBit(mask3, j - 1),                   newT + 1, ogmask1, ogmask2, ts);       }     }     if (j > 1) {       if (!checkBit(mask1, j - 1) && !checkBit(mask2, j - 1) &&           !checkBit(mask3, j - 1) && !checkBit(mask3, j) &&           !checkBit(mask3, j - 2)) {         long long newmask = setBit(mask3, j - 1);         newmask = setBit(newmask, j);         newmask = setBit(newmask, j - 2);         backtrack(j + 1, setBit(mask1, j - 1), setBit(mask2, j - 1), newmask,                   newT + 1, ogmask1, ogmask2, setBit(ts, 2 * (j - 1) + 1));       }     }     if (j > 1) {       if (!checkBit(mask1, j - 2) && !checkBit(mask3, j - 2) &&           !checkBit(mask2, j) && !checkBit(mask2, j - 1) &&           !checkBit(mask2, j - 2)) {         long long newmask = setBit(mask2, j);         newmask = setBit(newmask, j - 1);         newmask = setBit(newmask, j - 2);         backtrack(j + 1, setBit(mask1, j - 2), newmask, setBit(mask3, j - 2),                   newT + 1, ogmask1, ogmask2, setBit(ts, 2 * (j - 2)));       }     }     if (j > 1) {       if (!checkBit(mask1, j) && !checkBit(mask3, j) && !checkBit(mask2, j) &&           !checkBit(mask2, j - 1) && !checkBit(mask2, j - 2)) {         long long newmask = setBit(mask2, j);         newmask = setBit(newmask, j - 1);         newmask = setBit(newmask, j - 2);         ts = setBit(ts, 2 * j);         ts = setBit(ts, 2 * j + 1);         backtrack(j + 1, setBit(mask1, j), newmask, setBit(mask3, j), newT + 1,                   ogmask1, ogmask2, ts);         ts = unsetBit(ts, 2 * j);         ts = unsetBit(ts, 2 * j + 1);       }     }     backtrack(j + 1, mask1, mask2, mask3, newT, ogmask1, ogmask2, ts);   }   char currchar =  A ;   void recursion(long long i, long long mask1, long long mask2) {     if (i == 0) return;     recursion(i - 1, recur[i][mask1][mask2].first.first,               recur[i][mask1][mask2].first.second);     long long mask = insert[i][mask1][mask2];     for (long long j = 0; j < m; j++) {       if (!checkBit(recur[i][mask1][mask2].second, j)) {         ans[i][j] =  . ;         continue;       }       if (checkBit(mask, j * 2) && checkBit(mask, j * 2 + 1)) {         ans[i][j] = ans[i + 1][j] = ans[i + 2][j] = ans[i + 1][j - 1] =             ans[i + 1][j - 2] = currchar;         currchar++;       } else if (checkBit(mask, j * 2) && !checkBit(mask, j * 2 + 1)) {         ans[i][j] = ans[i + 1][j + 2] = ans[i + 2][j] = ans[i + 1][j + 1] =             ans[i + 1][j] = currchar;         currchar++;       } else if (!checkBit(mask, j * 2) && checkBit(mask, j * 2 + 1)) {         ans[i][j] = ans[i + 1][j] = ans[i + 2][j + 1] = ans[i + 2][j - 1] =             ans[i + 2][j] = currchar;         currchar++;       }     }   }   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     cin >> n >> m;     memset(dp, -1, sizeof(dp));     memset(ans, 0, sizeof(ans));     dp[0][0][0] = 0;     for (long long i = 0; i < n; i++) {       curr = i;       nexty = i + 1;       for (long long mask1 = 0; mask1 < (1 << m); mask1++) {         for (long long mask2 = 0; mask2 < (1 << m); mask2++) {           if (dp[curr][mask1][mask2] != -1) {             backtrack(0, mask1, mask2, 0, 0, mask1, mask2, 0);           }         }       }     }     cout << dp[n][0][0] <<   n ;     recursion(n, 0, 0);     for (long long i = 1; i <= n; i++) {       for (long long j = 0; j < m; j++) {         if (ans[i][j] == 0 && ans[i][j - 1] == 0 && ans[i][j + 1] == 0 &&             ans[i + 1][j] == 0 && ans[i + 2][j] == 0) {           ans[i][j] = ans[i][j - 1] = ans[i][j + 1] = ans[i + 1][j] =               ans[i + 2][j] = currchar;           currchar++;         }       }     }     for (long long i = 1; i <= n; i++) {       for (long long j = 0; j < m; j++) cout << ans[i][j];       cout <<   n ;     }   }   