Valmiki Ramayana Aranya Kanda Sarga 5 Shloka 37
Original Shlokaइमां मन्दाकिनीं राम प्रतिस्रोतामनुव्रज। नदीं पुष्पोडुपवहां ततस्तत्र गमिष्यसि।।3.5.37।।
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राम O Rama, स पुष्पोडुपवहाम् carrying flowers and floats, इमाम् this, मन्दाकिनीम् river Mandakini, प्रतिस्रोताम् against the current, अनुव्रज follow, ततः then, तत्र there, गमिष्यसि you will reach.
Proceed, O Rama in the reverse direction of the river Mandakini carrying flowers and floats. And you will reach the place.