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  1. #include <bits/stdc++.h>
  2.  
  3. typedef long long ll;
  4. using namespace std;
  5.  
  6. #define N 1000001
  7. int phi[N];
  8. ll a[N];
  9. #define GC getchar_unlocked()
  10. int scan() {
  11.   int ret = 0;
  12.   int ip = GC;
  13.   for (; ip < '0' || ip > '9'; ip = GC)
  14.     ;
  15.   for (; ip >= '0' && ip <= '9'; ip = GC)
  16.     ret = ret * 10 + ip - '0';
  17.   return ret;
  18. }
  19.  
  20. int main() {
  21.   int i, j, n;
  22.   for (i = 1; i < N; i++)
  23.     phi[i] = i;
  24.   phi[1] = 0;
  25.   for (i = 2; i < N; i++)
  26.     if (phi[i] == i)
  27.       for (j = i; j < N; j += i)
  28.         phi[j] -= phi[j] / i;
  29.   for (i = 1; i < N; i++) {
  30.     for (j = i; j < N; j += i) {
  31.       a[j] += (i * phi[(j / i)]);
  32.     }
  33.   }
  34.   for (i = 2; i < N; i++)
  35.     a[i] += a[i - 1];
  36.   while (1) {
  37.     n = scan();
  38.     assert(n < N);
  39.     if (n == 0)
  40.       break;
  41.     printf("%lld\n", a[n]);
  42.   }
  43.   return 0;
  44. }
Success #stdin #stdout 0.07s 15192KB
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https://ideone.com/XN7kqo
language:
C++ (gcc 8.3)
created:
8 years ago
visibility:
secret

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