#include <stdio.h>
int main()
{ int hi=10000000,p,mid,lo=1,e=0;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
  scanf("%d",&p);
  while(lo<=hi)
  { mid=lo+(hi-lo)/2;
       int 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;
     else if(p==e) return mid;
     }
   return 0;
}