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.stdio; immutable int INF = 1 << 28; void main() { auto s = readln.split.map!(to!int); auto N = s[0]; auto M = s[1]; auto edges = new int[][](N); foreach (i; 0..M) { s = readln.split.map!(to!int); edges[s[0] - 1] ~= s[1] - 1; edges[s[1] - 1] ~= s[0] - 1; } auto VU = new bool[int][](N); foreach (u; edges[0]) { foreach (v; edges[u]) { if (v != 0) VU[v][u] = true; } } bool ok = false; foreach (i; 1..N) { foreach (j; edges[i]) { bool ij, ji; if (j in VU[i]) VU[i].remove(j), ij = true; if (i in VU[j]) VU[j].remove(i), ji = true; auto il = VU[i].keys.length; auto jl = VU[j].keys.length; if (il == 1 && jl == 1 && VU[i].keys[0] != VU[j].keys[0]) ok = true; if (il > 0 && jl > 0 && max(il, jl) > 1) ok = true; if (ij) VU[i][j] = true; if (ji) VU[j][i] = true; } } writeln(ok ? "YES" : "NO"); }