#include <stdio.h>


int n;
int nrz(int n);
long bincaut(long  a,long long b,int p) {
     long  long mid;
     while (a<=b) {
       mid= (a+b)/2;
        if (nrz(mid) >  p)
        b = mid;
       else if (nrz(mid) < p)
          a = mid;
       else
          return mid;        
  }  
  return -1;      
}
     
int nrz( int n)
{
     long p = 0;
     while( n )
     {
            p += n/5;
            n /= 5;
     }
     return p;
}

int main() {
  freopen("factorial.in","r",stdin);
  freopen("factorial.out","w",stdout);
  scanf("%d",&n);
  printf("%ld",bincaut(1,10000000000000000LL,n));
  
}