#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int n,p;
int f(int n)
{
    int r=0,p5=5;
    while(n>=p5)
    {
        r=r+n/p5;
        p5=p5*5;
    }
    return r;
}
int main()
{
    int i;
    in>>p;
    int st=1,dr=500000000;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(f(mij)<p)
            st=mij+1;
        else
            dr=mij-1;
    }
    if(f(st)==p)
        out<<st;
    else
        out<<"-1";
    return 0;
}