#include    <iostream>
#include    <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int P,N,nr,c=1;
int main()
{
    fin>>P;
    if (P<0) N=-1;
    else if (P==0) N=1;
    else
    while(nr!=P)
    {
        while(c%5==0)
        {
            c/=5;
            nr++;
        }
        N+=5;
        c=N;
    }
    if(N>1) N-=5;
    fout<<N;
    return 0;
}