#include <iostream>
#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");


long long st,dr,mij,p,sol;

long long vrf(int x)
{
    long long nr=0;
    while(x>5)
    {
        nr+=x/5;
        x/=5;
    }
    return nr;
}
int main()
{
    f>>p;
    if(p==0)g<<1;
        else
        {
            st=1;
            dr=500000000;
            sol=-1;
            while(st<=dr)
            {
                mij=(st+dr)/2;
                if(vrf(mij)>p)dr=mij-1;
                    else if(vrf(mij)<p)st=mij+1;
                        else {sol=mij;dr=mij-1;}

        }
        g<<sol;
}
return 0;
}