#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p,ls,ld,x,mij,s,lg[12000000];
int p5(int x)
{
    int s=0;
    while(x%5==0 && x)
    {
        x/=5;
        s+=1;
    }
    return s;
}
int verif(int x)
{
    int s=0;
    for(int i=5;i<=x;i+=5)s+=p5(i);
    return s;
}
int main()
{
    fin>>p;
    ls=1;
    ld=12000000;
    while(ls<ld)
    {
        mij=(ls+ld)/2;
        if(verif(mij)>=p)ld=mij;
        else ls=mij+1;
    }
    if(verif(ls)==p)fout<<ls;
    else fout<<-1;
    return 0;
}