#include <bits/stdc++.h>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
long long p;
void citire()
{
    in>>p;
}
long long nz(long long n)
{
    long long pa=0,pb=0,p2=2,p5=5;
    while(p2<=n)
    {
        pa+=n/p2;
        p2*=2;
    }
    while(p5<=n)
    {
        pb+=n/p5;
        p5*=5;
    }
    return min(pa,pb);
}
void rez()
{
    long long st,dr,mij,ans=-1;
    st=1;
    dr=1e18;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(nz(mij)<p)
        {
            st=mij+1;
        }
        else
            if(nz(mij)>p)
        {
            dr=mij-1;
        }
        else
        {
            ans=mij;
            dr=mij;
        }
    }
    out<<ans;
}
int main()
{
    citire();
    rez();
    return 0;
}