26 lines
398 B
ObjectPascal
26 lines
398 B
ObjectPascal
var
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f:array[1..1000]of longint;
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i,n,p:longint;
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procedure setio;
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begin
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assign(input,'surface.in');
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assign(output,'surface.out');
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reset(input);
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rewrite(output);
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end;
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procedure print;
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begin
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close(input);
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close(output);
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end;
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begin
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setio;
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readln(n,p);
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f[p]:=2*p;
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for i:=p+1 to n do
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f[i]:=f[i-1]+i;
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writeln(f[n]);
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print;
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end.
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