#include <fstream>
#define Capat 100000000000000000
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long n;
long long numar(long long y){
    long long s=0,p=1;
    while(y/p > 0){
        p *= 5;
        s += y/p;
    }
    return s;
}
long long caut(long long x){
    long long left = 1 , right = Capat;
    long long mij=Capat/2;
    while(left <= right){
        mij = (left + right)/2;
        if(numar(mij)==x)
            return mij;
        else
        if(numar(mij) < x)
            left = mij + 1;
        else
        if(numar(mij) > x)
            right = mij - 1;
    }
}
int main()
{
    f >> n;
    long long nr = caut(n);
    if(nr!=0)
    {
        while(nr>0 && numar(nr)==n)
            nr--;
        g<<nr+1;
    }
    else
        g<<-1;
    return 0;
}