#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int main()
{
    int n,m,p,nr,rez=-1,st,dr;
    cin>>n;
    st=1;
    dr=1000000000;
    while(st<=dr)
    {
        m=(st+dr)/2;
        p=1;
        nr=0;
        while(p<=m)
        {
            p*=5;
            nr+=m/p;

        }
        if(nr<n)
            st=m+1;
        else
        if(nr>n)
            dr=m-1;
        else{
            rez=m;
            dr=m-1;
        }
    }
    cout<<rez;
    return 0;
}