#include<stdio.h>
#include<iostream.h>
#define MAX 100000000

typedef long long LL;

LL p,i,j,m,sol;

int f(LL c)
{
     long p = 0;
     while( c )
     {
	    p += c/5;
	    c /= 5;
     }
     return p;
}



int main()
{
  freopen("fact.in","r",stdin);
  freopen("fact.out","w",stdout);

    scanf("%lld",&p);

    for( i=1,j=MAX,sol=-1; i<=j; )

    { m = (i+j)/2;

      if( f(m) > p ) { j = m-1; continue; }

      if( f(m) < p ) { i = m+1; continue; }

      sol = m; j=m-1;  }


    printf("%lld\n",sol);

  return 0;    }