#include<cstdio>
using namespace std;
int p,p1,ls,ld,m,pr,z;
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
        scanf("%d",&p);
        ls=1;
        ld=2000000000;
        p1=p;
    while (ls<=ld)
    {
        p=p1;
         m=(ls+ld)/2;
        z=0;
        pr=5;
        while (z<=p && pr<=m)
        {
            z=z+(m/pr);
            pr*=5;
        }
        if (z==p)
        {
            while (m%5) m--;
            printf("%d\n",m);
            return 0;
        }
        if (z>p)
        {
            ld=m-1;
        }
        if (z<p) ls=m+1;
    }
    printf("-1\n");
    return 0;
}