ll c[1005][1005]; 
const int mod=1e9+7;
    
for (int i=0; i<=1000; ++i)
{
    c[i][0]=c[i][i]=1;
    for (int j=1; j<i; ++j)
        c[i][j]=(c[i-1][j]+c[i-1][j-1])%mod;
}