import std.stdio, std.array, std.string, std.conv, std.algorithm; import std.typecons, std.range, std.random, std.math, std.container; import std.numeric, std.bigint, core.bitop, core.stdc.string; void main() { auto s = readln.split.map!(to!int); auto H = s[0]; auto W = s[1]; auto A = H.iota.map!(_ => readln.chomp).array; Tuple!(int, int)[] B; foreach (i; 0..H) foreach (j; 0..W) if (A[i][j] == 'o') B ~= tuple(i, j); auto cnt = new int[](2); foreach (i; 0..B.length) cnt[(B[i][0] + B[i][1]) % 2] += 1; if (B.length == 0) { writeln("YES"); } else if (B.length == 1) { writeln("NO"); } else if (B.length == 2) { writeln(cnt[0] == 1 ? "YES" : "NO"); } else if (B.length == 3) { assert(false); } else { writeln(cnt[0] <= 1 || cnt[1] <= 1 ? "NO" : "YES"); } }