#include <bits/stdc++.h>
#define int long long

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n;
int factzero(int x)
{
    int rez = 0;
    int put = 5;
    while(put<=x)
    {
        rez+=x/put;
        put = 1LL*put*5;
    }
    return rez;
}
signed main()
{
    f>>n;
    int st = 1;
    int dr = 1000000000000000000;
    int rez = -1;
    while(st<=dr)
    {
        int mij = (st+dr)>>1;
        if(factzero(mij)>=n)
        {
            rez = mij;
            dr = mij-1;
        }
        else
        {
            st = mij+1;
        }
    }
    g<<rez<<'\n';
    return 0;
}