#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p,st=1,dr=1000000000000000000,n=-1,mid,nr,aux;
int main()
{
    fin>>p;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        nr=0;
        aux=mid;
        while(aux!=0)
        {
            nr+=aux/5;
            aux/=5;
        }
        if(nr>p)
            dr=mid-1;
        if(nr==p)
        {
            dr=mid-1;
            n=mid;
        }
        if(nr<p)
            st=mid+1;
    }
    fout<<n;
    return 0;
}