#include<fstream>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int main(){
    int p, m, s, n;
    fin >> p;
    for (n = 4*p;s < p;n++)
        for(m = n, s = 0;m;m /= 5, s += m);
    if (s-p)
        fout << -1;
    else if (p)
        fout << n-1;
    else fout << 1;
    return 0;
}