#include "bits/stdc++.h"
using namespace std;
 
#define ll long long
 
#define       forn(i,n)              for(int i=0;i<n;i++)
#define          all(v)              v.begin(), v.end()
#define         rall(v)              v.rbegin(),v.rend()
 
#define            pb                push_back
#define          sz(a)               (int)a.size()


ll count0(ll n){
    ll ans = 0;
    for(ll i = 5;i <= n; i *= 5){
        ans += n / i;
    }
    return ans;
}
void solve()
{ 
    ll ans = -1, l = 1, r = 1e13, p;
    cin >> p;

    while(l <= r){
        ll mid = l + (r - l) / 2;
        if(count0(mid) >= p){
            ans = mid;
            r = mid - 1;
        } else l = mid + 1;
    }
    cout << ans;
}   
 
int32_t main(){
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
}