// Problema factorial

#include <stdio.h>

int main()
{
    long p;
    freopen( "fact.in", "rt", stdin );
             scanf( "%ld", &p );
    fclose( stdin );
    
    long n, m, s, pt;
    n = 0;
    s = 5;
    pt = 0;
    while( p )
    {
           n = n+5;           
           p--;
           if( n == s ) { p-= pt; s *=5; pt++; }
    }
    
    freopen( "fact.out", "wt", stdout );
             printf( "%ld\n", n );
    fclose( stdout );
    return 0;
}