#include int main(){ int i,j,s=0; for(i=1;i<=100;i++) s+=i%2==0?(-1)*i:i; printf("%d\n",s); return 0;}
#include int main(){ int i,j=1,s=0; for(i=1;i<=100;i++){ s+=i*j; j=j*-1;}printf("%d\r\n",s); return 0;}