#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p, st, dr, mid;

int zero(int n) {
    int p = 5, s = 0;
    while (p<=n) {
        s += n/p;
        p*=5;
    }
    return s;

}

int main(){
    fin>>p;

    st = 1;
    dr = 5*p;

    while (st <= dr) {
        mid = (st+dr)/2;
        if (zero(mid) >= p)
            dr = mid-1;
        else
            st = mid+1;
    }
    if (zero(st) == p)
        fout<<st;
    else
        fout<<-1;



    return 0;
}