for循环不知道怎么运行，运行几次答案不对，求解

#include<bits/stdc++.h>
using namespace std;

int main() {
    int x=1,y=2;
    int sum=0;
    for(;x<=99;)
    {
        sum+=x*y;
        x+=2;
        y+=2;
    }
    cout<<sum<<endl;
    return 0;
}