#include<fstream>
#include<iostream>
#include<climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int p,i=1,OK=0,j=LONG_MAX,m,k,x;
    fin>>p;
    if(p==0)fout<<"1";
    while(i<=j&&OK==0)
	{
		m=(i+j)/2;
        x=5;
	    k=0;
	    while(x<=m){k=k+m/x;
	                x=x*5;}
	    if(k==p)OK=1;
	    else if(k>p)j=m-1;
	    else i=m+1;
    }
    if(OK==0)fout<<"-1";
    else {
        while(m%5!=0)m--;
        fout<<m;
        }
    fin.close();
    fout.close();
    return 0;
}