#include <cstdio>
#define MAX 800000000
using namespace std;

int main()
{
    freopen("factorial.in", "r", stdin);
    freopen("factorial.out", "w", stdout);
    int p, l1, l2, mij, k, k1, f;
    scanf("%d", &p);
    l1=1;
    l2=MAX;
    while(l1<=l2)
    {
        k=0;
        mij=(l1+l2)/2;
        f=5;
        while(f<=mij)
        {
            k+=mij/f;
            f*=5;
        }
        if(k>=p)
            l2=mij-1;
        else l1=mij+1;
    }
    if(k==p)
        printf("%d", mij);
    else printf("-1");
    return 0;
}