#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{   long long cont=5,put=5;
    int n,sum=0;
    fin>>n;
    if(n==0){fout<<1;return 0;}
    while(sum<n)
    {
        sum=0;
        if(cont>put)put=put*5;
        int copie=put;
        while(copie!=1)
        {
            sum=sum+cont/copie;
            copie=copie/5;
        }
        cont=cont+5;
    }
    if(sum>n)fout<<-1;
    else fout<<cont-5;
    return 0;
}