#include <cstdio>

using namespace std;
int nr_cif(int n)
{
    int r,s=0;
    r=5;
    while(r<=n)
    {
        s=s+n/r;
        r=r*5;
    }
    return s;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p,n=0,st,dr,med;
    scanf("%d",&p);
    if(p){
    st=1;
    dr=p;
    while(nr_cif(n)!=p)
    {
        med=(st+dr)/2;
        if(nr_cif(n)>=med)
        {
            st=med;
        }
        else
            dr=med;
        n++;
    }
    if(nr_cif(n)==p)
    printf("%d",n);
    else
    printf("-1");}
    else
        printf("1");
    return 0;
}