#include <fstream>
#include<climits>
using namespace std;
ifstream fin ("fact.in");
ofstream fout ("fact.out");
long long int p;
int st=1, dr=INT_MAX, val, k, mij;
long long zero(int n)
{
    long long int nr=0, x=5;
    while(x<=n)
    {
        nr+=n/x;
        x*=5;
    }
    return nr;
}
int main()
{
    fin>>p;
    //fout<<zero(p);
   // fout<<st<<"\n";
    //fout<<dr<<"\n";
    k=-1;
    if(k==0){fout<<"1\n"; return 0;}
    while(st<=dr)
    {
        mij=(st+dr)/2;
        val=zero(mij);
        if(val==p)
        {
            k=mij;
            dr=mij-1;
        }
        if(val>p)dr=mij-1;
        if(val<p)st=mij+1;
    }
    fout<<k<<"\n";

    return 0;
}