要用exit()

#include<bits/stdc++.h> using namespace std; int main(){ int a,b,m,n,c=0,s=0; cin>>a>>b>>m>>n; s=a+b; c=a+b; for(int i=3;i<=n;i++){ c=a+b; s+=c; a=b; b=c; if(c>=m){ break; } } cout<<s; return 0; }