#include <bits/stdc++.h>
using namespace std;
int calculare(int nr)
{
    int countq=0;
    int putere=5;
    while(nr/putere>0)
    {
        countq=countq+nr/putere;
        putere*=5;
    }
    return countq;
}
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    int st,dr,mij;
    int p;
    fin>>p;
    st=1;
    dr=p*5;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(calculare(mij)<p) st=mij+1;
        else
            st=mij-1;
    }
    if(calculare(st)==p) fout<<st;
        else
        fout<<-1;
    cout<<'\n';
    return 0;
}