#include <cstdio>
#include <iostream>

using namespace std;

int nr_zero( int a, int x ){
  if( x > a )
    return 0;
  return a / x + nr_zero( a, x * 5 );
}

int cb( int p ){
  int st = 0, dr =1000000000;
  while( dr - st > 1 ){
    int med = ( dr + st ) >> 1;
    if( nr_zero(med, 5) < p )
      st = med;
    else
      dr = med;
  }
  return dr;
}

int main()
{
    freopen( "fact.in", "r", stdin );
    freopen( "fact.out", "w", stdout );
    int n;
    scanf( "%d", &n );
    printf( "%d", cb(n) );
}