#include <iostream>
#include <fstream>
using namespace std;
ifstream fisin("fact.in");
ofstream fisout("fact.out");

int main()
{
    int P,x;
    int j=0;
    fisin>>P;
    if(P==0)
    {
        fisout<<-1;
        return 0;
    }
    while (x<P || x!=P)
    {
        x=0;
        j++;int y=j;
        while(y!=0)
        {
            x += y/5;
            y=y/5;
        }
    }
    if(x>P)
    {
        fisout<<-1;
    }
    else
    {
        fisout<<j;
    }
}