#include <iostream>
#include <fstream>

using namespace std;

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

const int Nmax = 500000000;

int n, p;

void BinSearch(int l, int r){
    if (l > r)
        return;
    int mid = (l + r) >> 1;
    int x = 5, s = 0;
    while (x <= mid){
        s += mid / x;
        x *= 5;
    }
    if (s == p)
        n = mid;
    if (s < p)
        BinSearch(mid + 1, r);
    else
        BinSearch(l, mid - 1);
}

int main(){
    fin >> p;
    n = -1;
    BinSearch(1, Nmax);
    fout << n << '\n';
    return 0;
}