import std.stdio; import std.string; import std.conv; import std.typecons; import std.container.dlist; class DisjointSet{ int[] parent; this(int size){ parent = new int[size]; parent[] = -1; } void unite(int x, int y){ x = root(x); y = root(y); if(x == y) return; if(parent[x] > parent[y]){ auto t = x; x = y; y = t; } parent[x] += parent[y]; parent[y] = x; } bool same(int x, int y){ return root(x) == root(y); } int root(int x){ if(parent[x] < 0) return x; parent[x] = root(parent[x]); return parent[x]; } int size(int x){ return -parent[root(x)]; } } int N; int M; int[][] E; void main(){ auto s = readln.chomp.split; N = s[0].to!int; M = s[1].to!int; E = new int[][](N * 2); auto ds = new DisjointSet(N); for(auto m = 0; m < M; m++){ s = readln.chomp.split; auto a = s[0].to!int - 1; auto b = s[1].to!int - 1; E[a] ~= b + N; E[a + N] ~= b; E[b] ~= a + N; E[b + N] ~= a; ds.unite(a, b); } auto result = true; bool[int] results; for(auto n = 0; n < N; n++){ if(ds.root(n) in results) continue; auto r = dfs(n); if(!r){ result = false; break; } results[ds.root(n)] = true; } writeln(result ? "Yes" : "No"); } bool dfs(int n){ auto q = DList!(Tuple!(int, int))(); q.insertBack(tuple(0, n)); auto used = new bool[N * 2]; while(!q.empty){ auto t = q.front; q.removeFront; if(t[0] % 2 == 1 && t[1] == n + N) return true; if(used[t[1]]) continue; used[t[1]] = true; foreach(c; E[t[1]]){ q.insertBack(tuple(t[0] + 1, c)); } } return false; }