Dirichlet's Theorem on Arithmetic Progressions--POJ 3006

#include<iostream>
using namespace std;
#define Max 1000010

bool prime[Max],flag;
int map[220],cnt;

void BuildTable()
{
    int i,j;
    prime[1]=false;
    prime[2]=prime[3]=true;
    for(i=2;i<1001;i++)
    {
        for(j=2;j*i<Max;j++)
        {
            prime[i*j]=false;
        }
    }
}
int main()
{
    int a,d,n,tmp;
    memset(prime,1,sizeof(prime));
    BuildTable();
    while(cin>>a>>d>>n && (a||d||n))
    {
        cnt=0;
        tmp=a;
        while(cnt!=n)
        {
            if(prime[tmp])
                map[++cnt]=tmp;
            tmp+=d;
        }
        cout<<map[n]<<endl;
    }
    return 1;
}