ttt<-c(1,3,4,4,6,8,2,4,5,9)
 ttt.status<-c(1,1,1,1,1,1,0,0,0,0)
 sfit<-survfit(Surv(ttt,ttt.status)~1,type="kaplan-meier",
               error="greenwood")
 summary(sfit)

 Call: survfit(formula = Surv(ttt, ttt.status) ~ 1)


  time n.risk n.event survival std.err lower 95% CI
     1     10       1    0.900  0.0949       0.7320
     3      8       1    0.788  0.1340       0.5641
     4      7       2    0.562  0.1651       0.3165
     6      3       1    0.375  0.1885       0.1400
     8      2       1    0.188  0.1627       0.0342