Smallest multiple

#include<iostream>
#include<algorithm>
using namespace std;
int lcm(int a ,int b)
{
    int big=max(a,b);
    int small=min(a,b);
    int max=a*b;
    for(int i=big; i<max; i+=big)
    {
        if(i%small==0)
            return i;
    }
    return max;
}
int main()
{
    int sum,a=1,b=2;
    while(b!=20)
    {
       sum=lcm(a,b);
       a=sum;
       b++;
    }
    cout<<sum<<endl;
    return 0;
}