#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int p,x,s;
int main()
{
    in>>p;
    int st=0,dr=1000000000,mij;
    while(st<dr)
    {
        mij=(st+dr)/2;
        x=mij;
        s=0;
        while(x)
        {
            s+=x/=5;
        }
        if(s>=p)dr=mij;
        else st=mij+1;
    }
    int aux=dr,rez=0;
    while(aux)
    {
        rez+=aux/=5;
    }
    if(rez==p)out<<dr;
    else out<<-1;
    return 0;
}