// Problema factorial

#include <stdio.h>

int main()
{
    long p;
    freopen( "fact.in" , "rt", stdin );
             scanf( "%ld", &p );
    fclose( stdin );
    
    long fac = 1, s = 0;    
    while( p > 0 )
    {
           s++;
           p--;
           fac = 5*s;
           if( s%5 == 0 ) p -= s/5;
    }
    
    freopen( "fact.out", "wt", stdout );
             printf ( "%ld", fac );
    fclose( stdout );
    return 0;    
}