#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p1,p,u,mij,t;
int raspuns(int x)
{
    int rasp=0;
    for (int i=5;i<=x;i*=5)
    {
        rasp+=x/i;
    }
    return rasp;
}
int main()
{fin>>p;
//5 in n! sa zic trebuie sa dea p
if (p==0) fout<<1;
else{
    p1=1;
    u=100000001;
    while (p1<=u)
    {
        mij=(p1+u)/2;
        if (raspuns(mij)>=p) {t=mij;u=mij-1;}
        else p1=mij+1;
    }
    if (t>0) fout<<t;
    else fout<<"-1";}
    return 0;
}