foo.cc: In function 'int main()':
foo.cc:9:21: warning: iteration 10006 invokes undefined behavior [-Waggressive-loop-optimizations]
    9 |                 c[i]=(long long)i*(i-1)*(i-2)*(i-3)/24;
      |                 ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:8:22: note: within this loop
    8 |         for(int i=4;i<=maxn;i++)
      |                     ~^~~~~~

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