program test;
var
i,j:int64;
ans:extended;
begin
while true do //直接读入
begin
read(i);
if i=-1 then break; //读到-1就退出
inc(j); //用j记录个数
ans:=ans+i;
end;
ans:=ans/j; //计算平均值
write(ans:0:1);
end.
program test;
var
i,j:int64;
ans:extended;
begin
while true do //直接读入
begin
read(i);
if i=-1 then break; //读到-1就退出
inc(j); //用j记录个数
ans:=ans+i;
end;
ans:=ans/j; //计算平均值
write(ans:0:1);
end.