14 lines
205 B
C++
14 lines
205 B
C++
#include<cstdio>
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#include<string>
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#include<iostream>
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using namespace std;
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int main()
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{
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long n,p,i,m,s,f[600];
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cin>>n>>p;
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f[p]=2*p;
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for (i=p+1; i<=n; i++)
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f[i]=f[i-1]+i;
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cout<<f[n];
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}
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