#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
int zero (int x){
    int nr=0;
    nr=nr+x/5;
    nr=nr+x/25;
    nr=nr+x/125;
    nr=nr+x/625;
    nr=nr+x/3125;
    nr=nr+x/15625;
    nr=nr+x/78125;
    nr=nr+x/390625;
    nr=nr+x/1953125;
    nr=nr+x/9765625;
    nr=nr+x/48828125;
    nr=nr+x/244140625;
    return nr;
}
int main()
{
    int p,u,m,ok,P;
    f>>P;
    p = 1;
    u = 5*P;
    if(P==0){
            g<<1;
            return 0;
    }
    ok=0;
    while(p<=u) {
        m=p+(u-p)/2;
        if(zero(m)>P)
            u=m-1;
        else if(zero(m)==P){
            u=m-1;
            ok=1;
        }
        else
            p=m+1;
    }
    if(ok==0) g<<-1;
    else g<<p;
}