#include<stdio.h>
#include<stdlib.h>
#include<ctime>
FILE*g=fopen("minesweeper.out","w");
int n,t,i,ok,s,v[100];
double x;

int main () {
	
	
	n = 2; srand(time(0));
	
	for ( t = 1 ; t <= 200000000 ; ++t ){
		for ( i = 0 ; i < n ; ++i )
			v[i] = 0;
		while ( 1 ){
			int u = rand() % n;
			++v[u];
			if ( v[u] % 3 == 2 ){
				ok = 1; s = 0;
				for ( i = 0 ; i < n ; ++i ){
					if ( v[i] % 3 != 2 ){
						ok = 0; break ;
					}
					s += v[i];
				}
				if ( ok ){
					x += s; break ;
				}
			}
		}
	}
	
	x /= (t-1);
	
	fprintf(g,"%lf\n",x);
	
	fclose(g);
	
	return 0;
}