import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main{

	static Scanner s=new Scanner(System.in);

	public static void main(String __[]){
		input();
		solve();
	}

	private static void input(){
	}

	private static void solve(){
		System.out.println(BigDecimal.valueOf((s.nextLong()/5)*s.nextLong())
				.divide(s.nextBigDecimal(),14,RoundingMode.HALF_UP));
	}
}