#include<stdio.h>
int main()
{
FILE *f;
int nr=0,p,t=0,m=0,q;
f=fopen("fact.in","r");
fscanf(f,"%d",&p);
if(!p){f=fopen("fact.out","w"); fprintf(f,"%d",1);}
else{
fclose(f);
while(nr<p)
{
if(p>(nr+4)) {nr+=5;m+=5;t+=5;while(!(q%5)){q=q/5;nr++;}}
else {m+=p-nr;nr=p;}
}
f=fopen("fact.out","w");
if(nr==p) fprintf(f,"%d",m*5);
else fprintf(f,"%d",-1);}
return 0;}