[Error] no match for 'operator<' (operand types are 'man1' and 'man1')

#include<bits/stdc++.h>
using namespace std;
int n;
struct man1{
	string name;
	int year,month,day;
	int id;
}m[101];
bool cmp(man1 a,man1 b){
	if(a.year==b.year){
		if(a.month==b.month){
			if(a.day==b.day){
				return a.id>b.id;
			}else{
				return a.day<b.day;
			}
		}else{
			return a.month<b.month;
		}
	}else{
		return a.year<b.year;
	}
}
int main(){
/*
freopen (".in","r",stdin);
freopen (".out","w",stdout);
*/
cin>>n;
for(int i=1;i<=n;i++){
	cin>>m[i].name>>m[i].year>>m[i].month>>m[i].day;	
	m[i].id=i;
} 
sort(m+1,m+1+n);
for(int i=1;i<=n;i++) cout<<m[i].name<<endl;




/*
fclose(stdin);