#include <fstream>
using namespace std;
ifstream fi("fact.in");
ofstream fo("fact.out");

int p,rez;

int cinci(int a)
{
	int c=5;
	int rez=0;
	while(c<=a)
	{
		rez+=a/c;
		c*=5;
	}
	return rez;
}

int bs(int st,int dr)
{
	int m;
	if(st==dr&&cinci(st)!=p)
		return -1;
	m=(st+dr)/2;
	if(cinci(m)==p)
		return m;
	if(cinci(m)>p)
		bs(st,m-1);
	else
		bs(m,dr);
}
int main()
{
    fi>>p;
    rez=bs(1,100000000);
    fo<<rez<<'\n';
    return 0;
}