为什么答案是错的，鸡兔同笼

scanf("%d %d",&head,&feet);

for(c=0;c<=head;c++){
    for(r=0;r<=head;r++){
        if(r+c==head&&r*4+c*2==feet){
            leap=1;break;
        }
        
    }
}
if(leap) printf("chickens = %d; rabbits = %d",c,r);
else printf("No solution!");

return 0;    

}