[{"from": "human", "value": "Synthesize a molecule that matches the given characteristics. The molecule is a guanidinium ion obtained by monoprotonation of metformin. It is a conjugate acid of a metformin."}, {"from": "gpt", "value": "[H+1].[C][N][Branch1][C][C][C][=Branch1][C][=N][N][=C][Branch1][C][N][N]"}]