Valmiki Ramayana Kishkindha Kanda Sarga 10 Shloka 19

अयम् this, स्थितः इति waiting there, मत्वा तु thinking like that, अहम् I, दुरासदम् formidable, प्रविष्टः entered, तदा then, तत्र there, तम् him, मार्गमाणस्य in the process of searching, मे for me, संवत्सरः गतः one year was over.

'Presuming that Sugriva was waiting there, I entered the formidable cave. While I was searching for the demon there, one year passed.