#include <bits/stdc++.h>

using namespace std;
long long n, st=1, dr=1000;
int check(int nr)
{
    int nrZero=(nr/5)+(nr/25);
    cerr<<nr<<" "<<nrZero<<endl;
    return nrZero;
}
int main()
{
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    cin>>n;
    int rasp;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(check(mij)==n)
        {
            rasp=mij;
            break;
        }
        else
        {
            if(check(mij)<n)
                st=mij+1;
            else dr=mij-1;
        }
    }
    cout<<rasp-(rasp%5);
    return 0;
}