#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int nrzer(int x)
{
    int cnt = 0, i ;
    for(i=5;i<=x;i=i*5)
    {
        cnt += x/i;
    }
    return cnt;
}
int main()
{
    int x , st , dr , mij ;
    fin >> x;
    st = 1;
    dr = 500000000;
    while(st<=dr)
    {
        mij = (st + dr)/2;
        if(x > nrzer(mij))
            st = mij+1;
        else
            dr = mij-1;
    }
    if(nrzer(st)==x)
        fout<<st;
    else
        fout<<"-1";
    return 0;
}