#include<fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
long long p,rez = -1;
int main()
{
	cin >> p;
	long long st = 1,mid,dr = 100000010,aux1;
	while(st <= dr)
	{
		mid = st + dr;mid/=2;
		aux1 = 0;
		
		for(int i = 5; i <= mid; i *= 5)aux1+=(mid/i);
		if (aux1 == p) rez = mid, dr = mid-1;
		if (aux1 < p)
		{
			st = mid + 1;
		}else dr = mid - 1;
	}
	//if (rez == 100000010) cout << "-1";
	cout << rez;
}