#include <iostream>
# include<fstream>
#include<climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");




int nr0(int n)
{
    int nr=0,p=5;
    while(n>=p)
    {
        nr=nr+n/p;
        p=p*5;
    }
    return nr;
}
int main()
{
    int i,j,m,p,z,ok=0;
    fin>>p;
    i=1;
    j=INT_MAX;
    while(i<=j && ok==0)
    {
        m=(i+j)/2;
        z=nr0(m);
        if(z==p)ok=1;
        else if(z>p)j=m-1;
             else i=m+1;
    }
    if(p==0)fout<<1;
    else if(ok==1)
    {
        while(m%5!=0)m--;
        fout<<m;
    }
    else fout<<-1;

    return 0;

}