// Problema factorial

#include <stdio.h>

int main()
{
    long p, n;
    int m5 = 1;
    freopen( "fact.in", "rt", stdin );
             scanf( "%ld", &p );             
    fclose( stdin );
    
    for( n=25; n<=p*5; n *= 5 )
         {
               p-= m5;
               m5++;
         } 
    
    freopen( "fact.out", "wt", stdout );
             if( p == 0 ) printf( "1\n" );
             else printf( "%ld\n", p*5 );
    fclose( stdout );
    return 0;
}