#include<stdio.h>
#define N 100000000
long p,v[N+1],i,j,t,s,k,l=0;
int main()
{freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%ld",&p);
for(s=1;s<=N;s<<=1);
for(i=0;s;s>>=1)
if(s+i<=N)
       {j=5*(i+s),t=0;
       for(k=5;k<=j;k*=5)
             t=t+j/k;
       if(t<=p)
             i+=s,l=t;}
if(p==0)
       printf("1");
else
       if(l==p)
               printf("%ld",5*i);
       else
               printf("-1");
fclose(stdin);
fclose(stdout);
return 0;}