#include <fstream>
#include <iostream>

using namespace std;

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

int main()
{
    int p,m,s=0,n;
    fin>>p;
    for(n=4*p; s<p; n++)
        for(m=n,s=0; m; m/=5,s+=m);
    if(s-p)
        fout<<-1;
    else if(p)
        fout<<n-1;
    else fout<<1;
    return 0;
}