import std.stdio, std.conv, std.functional, std.string; import std.algorithm, std.array, std.container, std.range, std.typecons; import std.bigint, std.numeric, std.math, std.random; import core.bitop; string FMT_F = "%.10f"; static File _f; void file_io(string fn) { _f = File(fn, "r"); } static string[] s_rd; T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; } T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; } T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; } T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; } T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; } T[] RDA(T = long)(T fix = 0) { if (_f.isOpen) return _RDA!T(_f, fix); else return _RDA!T(fix); } size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;} size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; } void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); } bool inside(T)(T x, T b, T e) { return x >= b && x < e; } T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); } double euDist(T)(T[] a, T[] b) { auto c = a.dup; c[] -= b[]; c[] *= c[]; return sqrt(cast(double)c.sum); } double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; } double norm(double[] vec) { return sqrt(reduce!((a,b)=>a+b*b)(0.0, vec)); } double dotProd(double[] a, double[] b) { auto r = a.dup; r[] *= b[]; return r.sum; } long mod = 10^^9 + 7; //long mod = 998_244_353; //long mod = 1_000_003; void moda(ref long x, long y) { x = (x + y) % mod; } void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; } void modm(ref long x, long y) { x = (x * y) % mod; } void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); } void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); } void main() { auto H = RD; auto W = RD; bool isRotate = H > W; if (isRotate) swap(H, W); auto a = new long[][](H, W); foreach (i; 0..H) { auto S = RD!string; foreach (j; 0..W) { if (isRotate) a[j][i] = S[j]-'a'; else a[i][j] = S[j]-'a'; } } if (a[0][0] != a[H-1][W-1]) writeln(0); else { auto dp = new long[][][]((H+W)/2, H, H); dp[0][0][0] = 1; foreach (i; 0..dp.length-1) { auto len = min(i+1, H); foreach (j; 0..len) { auto y1 = j; auto x1 = i-j; foreach (k; 0..len) { if (dp[i][j][k] == 0) continue; auto y2 = H-i+k-1; auto x2 = W-k-1; if (a[y1][x1] != a[y2][x2]) continue; foreach (dd1, d1; [[0, 1], [1, 0]]) { auto dy1 = y1 + d1[0]; auto dx1 = x1 + d1[1]; if (!inside(dy1, 0, H) || !inside(dx1, 0, W)) continue; foreach (dd2, d2; [[1, 0], [0, 1]]) { auto dy2 = y2 - d2[0]; auto dx2 = x2 - d2[1]; if (!inside(dy2, 0, H) || !inside(dx2, 0, W)) continue; if (a[dy1][dx1] == a[dy2][dx2]) { dp[i+1][j+dd1][k+dd2].moda(dp[i][j][k]); } } } } } } debug writeln(dp); long ans; foreach (i; 0..H) ans.moda(dp[$-1][i][i]); writeln(ans); } stdout.flush; debug readln; }