#include <bits/stdc++.h>
#define ll long long
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int p;
ll fact(ll n)
{   ll nrz=0;
    ll d=5;
    while(d<=n)
    {   nrz+=n/d;
        d*=5;
    }
    return nrz;
}
int main()
{   f>>p;
    ll st=1;
    ll dr=(ll)(1<<30)*(1<<30);
    ll sol=-1;
    while(st<=dr)
    {   ll mij=(st+dr)/2;
        //g<<mij<<'\n';
        if(fact(mij)==p)
        {   sol=mij;
            dr=mij-1;
        }
        else
            if(fact(mij)<p) st=mij+1;
                else dr=mij-1;
    }
    g<<sol;
}