#include <stdio.h> #define MOD 1000000007LL typedef long long lli; lli d[1000001], c[1000001]; lli pw(lli n, lli x) { if(x==0) return 1; if(x%2) return n*pw(n,x-1)%MOD; else { lli ret=pw(n,x/2); return ret*ret%MOD; } } int main() { c[1]=1; for(lli i=2;i<=1000000;i++) { lli aa=(2*i-1)*(2*i)%MOD; lli bb=pw(i*(i+1)%MOD,MOD-2); c[i]=c[i-1]*aa%MOD*bb%MOD; } lli n, k; scanf("%lld %lld",&n,&k); d[1]=k; for(lli i=2;i<=n;i++) { if(i%2) d[i]=(d[i-1]*(k+1)%MOD-c[(i-1)/2]*pw(k,(i-1)/2)%MOD+MOD)%MOD; else d[i]=d[i-1]*(k+1)%MOD; } printf("%lld\n",d[n]); return 0; }

R.cpp: In function 'int main()':
R.cpp:23:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%lld %lld",&n,&k);
                          ^