#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll p, last;
ll nr(ll q){
    ll cnt = 0;
    for (ll i=5; i<=q; i*=5) cnt += q/i;
    return cnt;
}

int main(){
    ifstream cin ("fact.in");
    ofstream cout ("fact.out");
    cin >> p;
    int st = 1, dr = 1e9;
    while (st < dr){
        int mid = (st + dr) >> 1;
        if (nr(mid) >= p) dr = mid;
        else st = mid + 1;
    }
    if (nr(st) == p) return cout << st, 0;
    return cout << -1, 0;
}