#include <fstream>

using namespace std;

int nZero(int n)
{
    int nr=0,p=5;
 
    while(p<=n)
    {
        nr+=n/p;
        p*=5;
    }
 
    return nr;
}

ifstream f("fact.in");
ofstream g("fact.out");

int p;

int solve(int left, int right, int *final)
{
	if(left > right)
	{
		return 0;
	}

	int mid = (left+right)/2;
	
	int rez = nZero(mid);
	if(rez == p)
		*final = mid;
	if(rez >= p)
		solve(left, mid-1, final);
	else
		solve(mid+1, right, final);
}

int main()
{
	f >> p;	
	int x=-1;
	int rez = solve(1, 1000000000, &x);
	g << x;
	
}