#include<stdio.h>
int k,sol,n,l1,l2,ok,p;
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    l1=1;
    l2=100000000;
    ok=-1;
    while(l1<=l2)
    {
        n=(l1+l2)/2;
        int aux=n;
        k=5;
        sol=0;
         while(n/k>=1)
         {
              sol+=n/k;
              k=k*5;
         }
         if(sol==p)
             ok=aux;
         if(sol>=p)
             l2=aux-1;
          else l1=aux+1;
    }
    printf("%d",ok);
    return 0;
}