bs.d1=function(S,K,r,sigma,T) {
( log(S/K) + (r+sigma^2/2)*T ) / (sigma*sqrt(T))
}
bs.d2=function(S,K,r,sigma,T) {
bs.d1(S,K,r,sigma,T)-sigma*sqrt(T)
}
bs.call=function(S,K,r,sigma,T) {
d1 = ( log(S/K) + (r+sigma^2/2)*T ) / (sigma*sqrt(T))
d2 = d1 - sigma*sqrt(T)
S*pnorm(d1)-exp(-r*T)*K*pnorm(d2)
}
bs.call(100,200,0.05,0.35,0.5)