#include<stdio.h>
int main()
{
    int i,j,k,l,m,n,o,q,nr;
    long unsigned p;
    FILE *f; FILE *g;
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%lu",&p);
    if(p<0)
        fprintf(g,"%d",-1);
    if(p==0)
        fprintf(g,"%d",1);
    if(p==1)
       fprintf(g,"%d",5);
    if(p==2)
      fprintf(g,"%d",10); 
    if(p>2)
    {   
        o=0;
        for(m=10 ; m<=5*p ; m+=5)
        {
            q=m;
            while(q%5==0 && q!=0 && q%25==0)
            {
                q/=5;
                o++;
            }
            printf("o=%d\n",o);
        }
        if(p==5)
            fprintf(g,"%d",-1);
        else
        {
            fprintf(g,"%lu",5*p-o);
            printf("\n%lu\n",5*p-(o-1)*5);
        }
    }
return 0;
}