#include <stdio.h>
int bin(int p)
{ int hi=10000000,mid,lo=1,e,a;

  while(lo<=hi)
  { mid=lo+(hi-lo)/2;
       a=mid;e=0;
  while(a/5)
    { e+=a/5;
    a/=5;
}


    if(p<e) hi=mid-1;
   else if(p>e) lo=mid+1;
     if(p==e) return mid;
     }
   return -1;
}
int main()
{int n;
freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
  scanf("%d",&n);
  printf("%d",bin(n));
  return 0;
  }