菲波那切数列
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<script type="text/javascript">
var n = parseInt(window.prompt('input'));
var f = 1,
s = 1,
t;
if(n > 2){
for(var i = 0; i < n - 2 ; i++ ){
t = f + s;
f = s;
s = t;
}
document.write(t);
}else{
document.write(1);
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