rm(list=ls())
num.sample=10000
for(N in 1000:10000){

  aa=0

  for(i in 1:num.sample){  

    y1 = mean(rnorm(N,0,1))

    y2=mean( rnorm(N,0.2,1))


    if (abs(y1-y2)<0.23 )   
    {
      aa=aa+1
    }

    bb=aa/num.sample
  }
  if (bb > 0.8) break
}
N