#include <iostream>
#include<fstream>
#include<climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int p,m,i=1,k,j=LONG_MAX,ok=0,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;
    }
}