#include <bits/stdc++.h>
using namespace std;
int p;
void citire()
{
    cin>>p;
}
int nz(int n)
{
    int p2=2,p5=5,s1=0,s2=0;
    while(p2<=n)
    {
        s1+=n/p2;
        p2=p2*2;
        
    }
    while(p5<=n)
    {
        s2+=n/p5;
        p5=p5*5;
        
    }
    if(s1<=s2)
    {
        return s1;
    }
    else
    return s2;
}
void rez()
{
    int st=1,dr=1e18,ans,mij;
    int p2=2,p5=5,s1=0,s2=0;
    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-1;
        }
    }
    cout<<ans;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    citire();
    rez();
    return 0;
}